Move model operations from ProfileSyncService to ChangeProcessor.

TEST=ProfileSyncServiceTest, sync integration tests

Review URL: http://codereview.chromium.org/172040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@23669 0039d316-1c4b-4281-b951-d872f2087c98

11 files changed, 885 insertions, 693 deletions

diff --git a/chrome/browser/sync/glue/change_processor.cc b/chrome/browser/sync/glue/change_processor.cc
new file mode 100644
index 0000000..09ddb96
--- /dev/null
+++ b/chrome/browser/sync/glue/change_processor.cc
@@ -0,0 +1,541 @@
+// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifdef CHROME_PERSONALIZATION
+
+#include "chrome/browser/sync/glue/change_processor.h"
+
+#include "base/gfx/png_encoder.h"
+#include "base/string_util.h"
+#include "chrome/browser/bookmarks/bookmark_utils.h"
+#include "chrome/browser/profile.h"
+#include "chrome/browser/sync/profile_sync_service.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+
+namespace browser_sync {
+
+void ChangeProcessor::Start(BookmarkModel* model, sync_api::UserShare* handle) {
+  DCHECK(error_handler_ && model_associator_);
+  DCHECK(!share_handle_ && !bookmark_model_);
+  share_handle_ = handle;
+  bookmark_model_ = model;
+  DCHECK(model->IsLoaded());
+  bookmark_model_->AddObserver(this);
+  running_ = true;
+}
+
+void ChangeProcessor::Stop() {
+  if (!running_)
+    return;
+  DCHECK(bookmark_model_);
+  bookmark_model_->RemoveObserver(this);
+  bookmark_model_ = NULL;
+  share_handle_ = NULL;
+  model_associator_ = NULL;
+  running_ = false;
+}
+
+void ChangeProcessor::UpdateSyncNodeProperties(const BookmarkNode* src,
+                                               BookmarkModel* model,
+                                               sync_api::WriteNode* dst) {
+  // Set the properties of the item.
+  dst->SetIsFolder(src->is_folder());
+  dst->SetTitle(WideToUTF16(src->GetTitle()).c_str());
+  // URL is passed as a C string here because this interface avoids
+  // string16. SetURL copies the data into its own memory.
+  string16 url = UTF8ToUTF16(src->GetURL().spec());
+  dst->SetURL(url.c_str());
+  SetSyncNodeFavicon(src, model, dst);
+}
+
+// static
+void ChangeProcessor::EncodeFavicon(const BookmarkNode* src,
+                                    BookmarkModel* model,
+                                    std::vector<unsigned char>* dst) {
+  const SkBitmap& favicon = model->GetFavIcon(src);
+
+  dst->clear();
+
+  // Check for zero-dimension images.  This can happen if the favicon is
+  // still being loaded.
+  if (favicon.empty())
+    return;
+
+  // Re-encode the BookmarkNode's favicon as a PNG, and pass the data to the
+  // sync subsystem.
+  if (!PNGEncoder::EncodeBGRASkBitmap(favicon, false, dst))
+    return;
+}
+
+void ChangeProcessor::RemoveOneSyncNode(sync_api::WriteTransaction* trans,
+                                        const BookmarkNode* node) {
+  sync_api::WriteNode sync_node(trans);
+  if (!model_associator_->InitSyncNodeFromBookmarkId(node->id(), &sync_node)) {
+    error_handler_->OnUnrecoverableError();
+    return;
+  }
+  // This node should have no children.
+  DCHECK(sync_node.GetFirstChildId() == sync_api::kInvalidId);
+  // Remove association and delete the sync node.
+  model_associator_->DisassociateIds(sync_node.GetId());
+  sync_node.Remove();
+}
+
+
+void ChangeProcessor::RemoveSyncNodeHierarchy(const BookmarkNode* topmost) {
+  sync_api::WriteTransaction trans(share_handle_);
+
+  // Later logic assumes that |topmost| has been unlinked.
+  DCHECK(!topmost->GetParent());
+
+  // A BookmarkModel deletion event means that |node| and all its children were
+  // deleted. Sync backend expects children to be deleted individually, so we do
+  // a depth-first-search here.  At each step, we consider the |index|-th child
+  // of |node|.  |index_stack| stores index values for the parent levels.
+  std::stack<int> index_stack;
+  index_stack.push(0);  // For the final pop.  It's never used.
+  const BookmarkNode* node = topmost;
+  int index = 0;
+  while (node) {
+    // The top of |index_stack| should always be |node|'s index.
+    DCHECK(!node->GetParent() || (node->GetParent()->IndexOfChild(node) ==
+      index_stack.top()));
+    if (index == node->GetChildCount()) {
+      // If we've processed all of |node|'s children, delete |node| and move
+      // on to its successor.
+      RemoveOneSyncNode(&trans, node);
+      node = node->GetParent();
+      index = index_stack.top() + 1;      // (top() + 0) was what we removed.
+      index_stack.pop();
+    } else {
+      // If |node| has an unprocessed child, process it next after pushing the
+      // current state onto the stack.
+      DCHECK_LT(index, node->GetChildCount());
+      index_stack.push(index);
+      node = node->GetChild(index);
+      index = 0;
+    }
+  }
+  DCHECK(index_stack.empty());  // Nothing should be left on the stack.
+}
+
+void ChangeProcessor::BookmarkModelBeingDeleted(BookmarkModel* model) {
+  DCHECK(!running_) << "BookmarkModel deleted while ChangeProcessor running.";
+  bookmark_model_ = NULL;
+}
+
+void ChangeProcessor::BookmarkNodeAdded(BookmarkModel* model,
+                                        const BookmarkNode* parent,
+                                        int index) {
+  DCHECK(running_);
+  DCHECK(share_handle_);
+
+  // Acquire a scoped write lock via a transaction.
+  sync_api::WriteTransaction trans(share_handle_);
+
+  CreateSyncNode(parent, model, index, &trans, model_associator_,
+                 error_handler_);
+}
+
+// static
+int64 ChangeProcessor::CreateSyncNode(const BookmarkNode* parent,
+    BookmarkModel* model, int index, sync_api::WriteTransaction* trans,
+    ModelAssociator* associator, UnrecoverableErrorHandler* error_handler) {
+  const BookmarkNode* child = parent->GetChild(index);
+  DCHECK(child);
+
+  // Create a WriteNode container to hold the new node.
+  sync_api::WriteNode sync_child(trans);
+
+  // Actually create the node with the appropriate initial position.
+  if (!PlaceSyncNode(CREATE, parent, index, trans, &sync_child, associator,
+                     error_handler)) {
+    LOG(WARNING) << "Sync node creation failed; recovery unlikely";
+    error_handler->OnUnrecoverableError();
+    return sync_api::kInvalidId;
+  }
+
+  UpdateSyncNodeProperties(child, model, &sync_child);
+
+  // Associate the ID from the sync domain with the bookmark node, so that we
+  // can refer back to this item later.
+  associator->AssociateIds(child->id(), sync_child.GetId());
+
+  return sync_child.GetId();
+}
+
+
+void ChangeProcessor::BookmarkNodeRemoved(BookmarkModel* model,
+                                          const BookmarkNode* parent,
+                                          int index,
+                                          const BookmarkNode* node) {
+  DCHECK(running_);
+  RemoveSyncNodeHierarchy(node);
+}
+
+void ChangeProcessor::BookmarkNodeChanged(BookmarkModel* model,
+                                          const BookmarkNode* node) {
+  DCHECK(running_);
+  // We shouldn't see changes to the top-level nodes.
+  DCHECK_NE(node, model->GetBookmarkBarNode());
+  DCHECK_NE(node, model->other_node());
+
+  // Acquire a scoped write lock via a transaction.
+  sync_api::WriteTransaction trans(share_handle_);
+
+  // Lookup the sync node that's associated with |node|.
+  sync_api::WriteNode sync_node(&trans);
+  if (!model_associator_->InitSyncNodeFromBookmarkId(node->id(), &sync_node)) {
+    error_handler_->OnUnrecoverableError();
+    return;
+  }
+
+  UpdateSyncNodeProperties(node, model, &sync_node);
+
+  DCHECK_EQ(sync_node.GetIsFolder(), node->is_folder());
+  DCHECK_EQ(model_associator_->GetBookmarkNodeFromSyncId(
+            sync_node.GetParentId()),
+            node->GetParent());
+  // This node's index should be one more than the predecessor's index.
+  DCHECK_EQ(node->GetParent()->IndexOfChild(node),
+            CalculateBookmarkModelInsertionIndex(node->GetParent(),
+                                                 &sync_node));
+}
+
+
+void ChangeProcessor::BookmarkNodeMoved(BookmarkModel* model,
+                                        const BookmarkNode* old_parent,
+                                        int old_index,
+                                        const BookmarkNode* new_parent,
+                                        int new_index) {
+  DCHECK(running_);
+  const BookmarkNode* child = new_parent->GetChild(new_index);
+  // We shouldn't see changes to the top-level nodes.
+  DCHECK_NE(child, model->GetBookmarkBarNode());
+  DCHECK_NE(child, model->other_node());
+
+  // Acquire a scoped write lock via a transaction.
+  sync_api::WriteTransaction trans(share_handle_);
+
+  // Lookup the sync node that's associated with |child|.
+  sync_api::WriteNode sync_node(&trans);
+  if (!model_associator_->InitSyncNodeFromBookmarkId(child->id(), &sync_node)) {
+    error_handler_->OnUnrecoverableError();
+    return;
+  }
+
+  if (!PlaceSyncNode(MOVE, new_parent, new_index, &trans, &sync_node,
+                     model_associator_, error_handler_)) {
+    error_handler_->OnUnrecoverableError();
+    return;
+  }
+}
+
+void ChangeProcessor::BookmarkNodeFavIconLoaded(BookmarkModel* model,
+                                                const BookmarkNode* node) {
+  DCHECK(running_);
+  BookmarkNodeChanged(model, node);
+}
+
+void ChangeProcessor::BookmarkNodeChildrenReordered(
+    BookmarkModel* model, const BookmarkNode* node) {
+
+  // Acquire a scoped write lock via a transaction.
+  sync_api::WriteTransaction trans(share_handle_);
+
+  // The given node's children got reordered. We need to reorder all the
+  // children of the corresponding sync node.
+  for (int i = 0; i < node->GetChildCount(); ++i) {
+    sync_api::WriteNode sync_child(&trans);
+    if (!model_associator_->InitSyncNodeFromBookmarkId(node->GetChild(i)->id(),
+                                                       &sync_child)) {
+      error_handler_->OnUnrecoverableError();
+      return;
+    }
+    DCHECK_EQ(sync_child.GetParentId(),
+              model_associator_->GetSyncIdFromBookmarkId(node->id()));
+
+    if (!PlaceSyncNode(MOVE, node, i, &trans, &sync_child, model_associator_,
+                       error_handler_)) {
+      error_handler_->OnUnrecoverableError();
+      return;
+    }
+  }
+}
+
+// static
+bool ChangeProcessor::PlaceSyncNode(MoveOrCreate operation,
+                                    const BookmarkNode* parent,
+                                    int index,
+                                    sync_api::WriteTransaction* trans,
+                                    sync_api::WriteNode* dst,
+                                    ModelAssociator* associator,
+                                    UnrecoverableErrorHandler* error_handler) {
+  sync_api::ReadNode sync_parent(trans);
+  if (!associator->InitSyncNodeFromBookmarkId(parent->id(), &sync_parent)) {
+    LOG(WARNING) << "Parent lookup failed";
+    error_handler->OnUnrecoverableError();
+    return false;
+  }
+
+  bool success = false;
+  if (index == 0) {
+    // Insert into first position.
+    success = (operation == CREATE) ? dst->InitByCreation(sync_parent, NULL) :
+                                      dst->SetPosition(sync_parent, NULL);
+    if (success) {
+      DCHECK_EQ(dst->GetParentId(), sync_parent.GetId());
+      DCHECK_EQ(dst->GetId(), sync_parent.GetFirstChildId());
+      DCHECK_EQ(dst->GetPredecessorId(), sync_api::kInvalidId);
+    }
+  } else {
+    // Find the bookmark model predecessor, and insert after it.
+    const BookmarkNode* prev = parent->GetChild(index - 1);
+    sync_api::ReadNode sync_prev(trans);
+    if (!associator->InitSyncNodeFromBookmarkId(prev->id(), &sync_prev)) {
+      LOG(WARNING) << "Predecessor lookup failed";
+      return false;
+    }
+    success = (operation == CREATE) ?
+        dst->InitByCreation(sync_parent, &sync_prev) :
+        dst->SetPosition(sync_parent, &sync_prev);
+    if (success) {
+      DCHECK_EQ(dst->GetParentId(), sync_parent.GetId());
+      DCHECK_EQ(dst->GetPredecessorId(), sync_prev.GetId());
+      DCHECK_EQ(dst->GetId(), sync_prev.GetSuccessorId());
+    }
+  }
+  return success;
+}
+
+// Determine the bookmark model index to which a node must be moved so that
+// predecessor of the node (in the bookmark model) matches the predecessor of
+// |source| (in the sync model).
+// As a precondition, this assumes that the predecessor of |source| has been
+// updated and is already in the correct position in the bookmark model.
+int ChangeProcessor::CalculateBookmarkModelInsertionIndex(
+    const BookmarkNode* parent,
+    const sync_api::BaseNode* child_info) const {
+  DCHECK(parent);
+  DCHECK(child_info);
+  int64 predecessor_id = child_info->GetPredecessorId();
+  // A return ID of kInvalidId indicates no predecessor.
+  if (predecessor_id == sync_api::kInvalidId)
+    return 0;
+
+  // Otherwise, insert after the predecessor bookmark node.
+  const BookmarkNode* predecessor =
+      model_associator_->GetBookmarkNodeFromSyncId(predecessor_id);
+  DCHECK(predecessor);
+  DCHECK_EQ(predecessor->GetParent(), parent);
+  return parent->IndexOfChild(predecessor) + 1;
+}
+
+// ApplyModelChanges is called by the sync backend after changes have been made
+// to the sync engine's model.  Apply these changes to the browser bookmark
+// model.
+void ChangeProcessor::ApplyChangesFromSyncModel(
+    const sync_api::BaseTransaction* trans,
+    const sync_api::SyncManager::ChangeRecord* changes,
+    int change_count) {
+  if (!running_)
+    return;
+  // A note about ordering.  Sync backend is responsible for ordering the change
+  // records in the following order:
+  //
+  // 1. Deletions, from leaves up to parents.
+  // 2. Existing items with synced parents & predecessors.
+  // 3. New items with synced parents & predecessors.
+  // 4. Items with parents & predecessors in the list.
+  // 5. Repeat #4 until all items are in the list.
+  //
+  // "Predecessor" here means the previous item within a given folder; an item
+  // in the first position is always said to have a synced predecessor.
+  // For the most part, applying these changes in the order given will yield
+  // the correct result.  There is one exception, however: for items that are
+  // moved away from a folder that is being deleted, we will process the delete
+  // before the move.  Since deletions in the bookmark model propagate from
+  // parent to child, we must move them to a temporary location.
+  BookmarkModel* model = bookmark_model_;
+
+  // We are going to make changes to the bookmarks model, but don't want to end
+  // up in a feedback loop, so remove ourselves as an observer while applying
+  // changes.
+  model->RemoveObserver(this);
+
+  // A parent to hold nodes temporarily orphaned by parent deletion.  It is
+  // lazily created inside the loop.
+  const BookmarkNode* foster_parent = NULL;
+  for (int i = 0; i < change_count; ++i) {
+    const BookmarkNode* dst =
+        model_associator_->GetBookmarkNodeFromSyncId(changes[i].id);
+    // Ignore changes to the permanent top-level nodes.  We only care about
+    // their children.
+    if ((dst == model->GetBookmarkBarNode()) || (dst == model->other_node()))
+      continue;
+    if (changes[i].action ==
+        sync_api::SyncManager::ChangeRecord::ACTION_DELETE) {
+      // Deletions should always be at the front of the list.
+      DCHECK(i == 0 || changes[i-1].action == changes[i].action);
+      // Children of a deleted node should not be deleted; they may be
+      // reparented by a later change record.  Move them to a temporary place.
+      DCHECK(dst) << "Could not find node to be deleted";
+      const BookmarkNode* parent = dst->GetParent();
+      if (dst->GetChildCount()) {
+        if (!foster_parent) {
+          foster_parent = model->AddGroup(model->other_node(),
+                                          model->other_node()->GetChildCount(),
+                                          std::wstring());
+        }
+        for (int i = dst->GetChildCount() - 1; i >= 0; --i) {
+          model->Move(dst->GetChild(i), foster_parent,
+                      foster_parent->GetChildCount());
+        }
+      }
+      DCHECK_EQ(dst->GetChildCount(), 0) << "Node being deleted has children";
+      model->Remove(parent, parent->IndexOfChild(dst));
+      dst = NULL;
+      model_associator_->DisassociateIds(changes[i].id);
+    } else {
+      DCHECK_EQ((changes[i].action ==
+          sync_api::SyncManager::ChangeRecord::ACTION_ADD), (dst == NULL))
+          << "ACTION_ADD should be seen if and only if the node is unknown.";
+
+      sync_api::ReadNode src(trans);
+      if (!src.InitByIdLookup(changes[i].id)) {
+        LOG(ERROR) << "ApplyModelChanges was passed a bad ID";
+        error_handler_->OnUnrecoverableError();
+        return;
+      }
+
+      CreateOrUpdateBookmarkNode(&src, model);
+    }
+  }
+  // Clean up the temporary node.
+  if (foster_parent) {
+    // There should be no nodes left under the foster parent.
+    DCHECK_EQ(foster_parent->GetChildCount(), 0);
+    model->Remove(foster_parent->GetParent(),
+                  foster_parent->GetParent()->IndexOfChild(foster_parent));
+    foster_parent = NULL;
+  }
+
+  // We are now ready to hear about bookmarks changes again.
+  model->AddObserver(this);
+}
+
+// Create a bookmark node corresponding to |src| if one is not already
+// associated with |src|.
+const BookmarkNode* ChangeProcessor::CreateOrUpdateBookmarkNode(
+    sync_api::BaseNode* src,
+    BookmarkModel* model) {
+  const BookmarkNode* parent =
+      model_associator_->GetBookmarkNodeFromSyncId(src->GetParentId());
+  if (!parent) {
+    DLOG(WARNING) << "Could not find parent of node being added/updated."
+      << " Node title: " << src->GetTitle()
+      << ", parent id = " << src->GetParentId();
+    return NULL;
+  }
+  int index = CalculateBookmarkModelInsertionIndex(parent, src);
+  const BookmarkNode* dst = model_associator_->GetBookmarkNodeFromSyncId(
+      src->GetId());
+  if (!dst) {
+    dst = CreateBookmarkNode(src, parent, model, index);
+    model_associator_->AssociateIds(dst->id(), src->GetId());
+  } else {
+    // URL and is_folder are not expected to change.
+    // TODO(ncarter): Determine if such changes should be legal or not.
+    DCHECK_EQ(src->GetIsFolder(), dst->is_folder());
+
+    // Handle reparenting and/or repositioning.
+    model->Move(dst, parent, index);
+
+    // Handle title update and URL changes due to possible conflict resolution
+    // that can happen if both a local user change and server change occur
+    // within a sufficiently small time interval.
+    const BookmarkNode* old_dst = dst;
+    dst = bookmark_utils::ApplyEditsWithNoGroupChange(model, parent, dst,
+        UTF16ToWide(src->GetTitle()),
+        src->GetIsFolder() ? GURL() : GURL(src->GetURL()),
+        NULL);  // NULL because we don't need a BookmarkEditor::Handler.
+    if (dst != old_dst) {  // dst was replaced with a new node with new URL.
+      model_associator_->DisassociateIds(src->GetId());
+      model_associator_->AssociateIds(dst->id(), src->GetId());
+    }
+    SetBookmarkFavicon(src, dst, model->profile());
+  }
+
+  return dst;
+}
+
+// static
+// Creates a bookmark node under the given parent node from the given sync
+// node. Returns the newly created node.
+const BookmarkNode* ChangeProcessor::CreateBookmarkNode(
+    sync_api::BaseNode* sync_node,
+    const BookmarkNode* parent,
+    BookmarkModel* model,
+    int index) {
+  DCHECK(parent);
+  DCHECK(index >= 0 && index <= parent->GetChildCount());
+
+  const BookmarkNode* node;
+  if (sync_node->GetIsFolder()) {
+    node = model->AddGroup(parent, index, UTF16ToWide(sync_node->GetTitle()));
+  } else {
+    GURL url(sync_node->GetURL());
+    node = model->AddURL(parent, index,
+                         UTF16ToWide(sync_node->GetTitle()), url);
+    SetBookmarkFavicon(sync_node, node, model->profile());
+  }
+  return node;
+}
+
+// static
+// Sets the favicon of the given bookmark node from the given sync node.
+bool ChangeProcessor::SetBookmarkFavicon(
+    sync_api::BaseNode* sync_node,
+    const BookmarkNode* bookmark_node,
+    Profile* profile) {
+  size_t icon_size = 0;
+  const unsigned char* icon_bytes = sync_node->GetFaviconBytes(&icon_size);
+  if (!icon_size || !icon_bytes)
+    return false;
+
+  // Registering a favicon requires that we provide a source URL, but we
+  // don't know where these came from.  Currently we just use the
+  // destination URL, which is not correct, but since the favicon URL
+  // is used as a key in the history's thumbnail DB, this gives us a value
+  // which does not collide with others.
+  GURL fake_icon_url = bookmark_node->GetURL();
+
+  std::vector<unsigned char> icon_bytes_vector(icon_bytes,
+                                               icon_bytes + icon_size);
+
+  HistoryService* history =
+      profile->GetHistoryService(Profile::EXPLICIT_ACCESS);
+
+  history->AddPage(bookmark_node->GetURL());
+  history->SetFavIcon(bookmark_node->GetURL(),
+                      fake_icon_url,
+                      icon_bytes_vector);
+
+  return true;
+}
+
+// static
+void ChangeProcessor::SetSyncNodeFavicon(
+    const BookmarkNode* bookmark_node,
+    BookmarkModel* model,
+    sync_api::WriteNode* sync_node) {
+  std::vector<unsigned char> favicon_bytes;
+  EncodeFavicon(bookmark_node, model, &favicon_bytes);
+  if (!favicon_bytes.empty())
+    sync_node->SetFaviconBytes(&favicon_bytes[0], favicon_bytes.size());
+}
+
+}  // namespace browser_sync
+
+#endif  // CHROME_PERSONALIZATION
diff --git a/chrome/browser/sync/glue/change_processor.h b/chrome/browser/sync/glue/change_processor.h
new file mode 100644
index 0000000..e9b15d4
--- /dev/null
+++ b/chrome/browser/sync/glue/change_processor.h
@@ -0,0 +1,188 @@
+// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifdef CHROME_PERSONALIZATION
+
+#ifndef CHROME_BROWSER_SYNC_GLUE_CHANGE_PROCESSOR_H_
+#define CHROME_BROWSER_SYNC_GLUE_CHANGE_PROCESSOR_H_
+
+#include "chrome/browser/bookmarks/bookmark_model.h"
+#include "chrome/browser/sync/engine/syncapi.h"
+#include "chrome/browser/sync/glue/model_associator.h"
+#include "chrome/browser/sync/glue/sync_backend_host.h"
+
+class ProfileSyncService;
+
+namespace browser_sync {
+
+class UnrecoverableErrorHandler;
+
+// This class is responsible for taking changes from the BookmarkModel
+// and applying them to the sync_api 'syncable' model, and vice versa.
+// All operations and use of this class are from the UI thread.
+// This is currently bookmarks specific.
+class ChangeProcessor : public BookmarkModelObserver,
+                        public ChangeProcessingInterface {
+ public:
+  ChangeProcessor(UnrecoverableErrorHandler* error_handler)
+      : error_handler_(error_handler), model_associator_(NULL),
+        share_handle_(NULL), running_(false), bookmark_model_(NULL) {}
+  virtual ~ChangeProcessor() { Stop(); }
+
+  // Call when the processor should accept changes from either provided model
+  // and apply them to the other.  Both the BookmarkModel and sync_api are
+  // expected to be initialized and loaded.  You must have set a valid
+  // ModelAssociator and UnrecoverableErrorHandler before using this method,
+  // and the two models should be associated w.r.t the ModelAssociator provided.
+  // It is safe to call Start again after previously Stop()ing the processor.
+  void Start(BookmarkModel* model, sync_api::UserShare* handle);
+
+  // Call when processing changes between models is no longer safe / needed.
+  void Stop();
+
+  bool IsRunning() const { return running_; }
+
+  // Injectors for the components required to Start the processor.
+  void set_model_associator(ModelAssociator* associator) {
+    model_associator_ = associator;
+  }
+
+  // BookmarkModelObserver implementation.
+  // BookmarkModel -> sync_api model change application.
+  virtual void Loaded(BookmarkModel* model) { NOTREACHED(); }
+  virtual void BookmarkModelBeingDeleted(BookmarkModel* model);
+  virtual void BookmarkNodeMoved(BookmarkModel* model,
+                                 const BookmarkNode* old_parent,
+                                 int old_index,
+                                 const BookmarkNode* new_parent,
+                                 int new_index);
+  virtual void BookmarkNodeAdded(BookmarkModel* model,
+                                 const BookmarkNode* parent,
+                                 int index);
+  virtual void BookmarkNodeRemoved(BookmarkModel* model,
+                                   const BookmarkNode* parent,
+                                   int index,
+                                   const BookmarkNode* node);
+  virtual void BookmarkNodeChanged(BookmarkModel* model,
+                                   const BookmarkNode* node);
+  virtual void BookmarkNodeFavIconLoaded(BookmarkModel* model,
+                                         const BookmarkNode* node);
+  virtual void BookmarkNodeChildrenReordered(BookmarkModel* model,
+                                             const BookmarkNode* node);
+
+  // sync_api model -> BookmarkModel change application.
+  virtual void ApplyChangesFromSyncModel(
+      const sync_api::BaseTransaction* trans,
+      const sync_api::SyncManager::ChangeRecord* changes,
+      int change_count);
+
+  // The following methods are static and hence may be invoked at any time,
+  // and do not depend on having a running ChangeProcessor.
+  // Creates a bookmark node under the given parent node from the given sync
+  // node. Returns the newly created node.
+  static const BookmarkNode* CreateBookmarkNode(
+      sync_api::BaseNode* sync_node,
+      const BookmarkNode* parent,
+      BookmarkModel* model,
+      int index);
+
+  // Sets the favicon of the given bookmark node from the given sync node.
+  // Returns whether the favicon was set in the bookmark node.
+  // |profile| is the profile that contains the HistoryService and BookmarkModel
+  // for the bookmark in question.
+  static bool SetBookmarkFavicon(sync_api::BaseNode* sync_node,
+                                 const BookmarkNode* bookmark_node,
+                                 Profile* profile);
+
+  // Sets the favicon of the given sync node from the given bookmark node.
+  static void SetSyncNodeFavicon(const BookmarkNode* bookmark_node,
+                                 BookmarkModel* model,
+                                 sync_api::WriteNode* sync_node);
+
+  // Treat the |index|th child of |parent| as a newly added node, and create a
+  // corresponding node in the sync domain using |trans|.  All properties
+  // will be transferred to the new node.  A node corresponding to |parent|
+  // must already exist and be associated for this call to succeed.  Returns
+  // the ID of the just-created node, or if creation fails, kInvalidID.
+  static int64 CreateSyncNode(const BookmarkNode* parent,
+                              BookmarkModel* model,
+                              int index,
+                              sync_api::WriteTransaction* trans,
+                              ModelAssociator* associator,
+                              UnrecoverableErrorHandler* error_handler);
+
+ private:
+  enum MoveOrCreate {
+    MOVE,
+    CREATE,
+  };
+
+  // Create a bookmark node corresponding to |src| if one is not already
+  // associated with |src|.  Returns the node that was created or updated.
+  const BookmarkNode* CreateOrUpdateBookmarkNode(
+      sync_api::BaseNode* src,
+      BookmarkModel* model);
+
+  // Helper function to determine the appropriate insertion index of sync node
+  // |node| under the Bookmark model node |parent|, to make the positions
+  // match up between the two models. This presumes that the predecessor of the
+  // item (in the bookmark model) has already been moved into its appropriate
+  // position.
+  int CalculateBookmarkModelInsertionIndex(
+      const BookmarkNode* parent,
+      const sync_api::BaseNode* node) const;
+
+  // Helper function used to fix the position of a sync node so that it matches
+  // the position of a corresponding bookmark model node. |parent| and
+  // |index| identify the bookmark model position.  |dst| is the node whose
+  // position is to be fixed.  If |operation| is CREATE, treat |dst| as an
+  // uncreated node and set its position via InitByCreation(); otherwise,
+  // |dst| is treated as an existing node, and its position will be set via
+  // SetPosition().  |trans| is the transaction to which |dst| belongs. Returns
+  // false on failure.
+  static bool PlaceSyncNode(MoveOrCreate operation,
+                            const BookmarkNode* parent,
+                            int index,
+                            sync_api::WriteTransaction* trans,
+                            sync_api::WriteNode* dst,
+                            ModelAssociator* associator,
+                            UnrecoverableErrorHandler* error_handler);
+
+  // Copy properties (but not position) from |src| to |dst|.
+  static void UpdateSyncNodeProperties(const BookmarkNode* src,
+                                       BookmarkModel* model,
+                                       sync_api::WriteNode* dst);
+
+  // Helper function to encode a bookmark's favicon into a PNG byte vector.
+  static void EncodeFavicon(const BookmarkNode* src,
+                            BookmarkModel* model,
+                            std::vector<unsigned char>* dst);
+
+  // Remove the sync node corresponding to |node|.  It shouldn't have
+  // any children.
+  void RemoveOneSyncNode(sync_api::WriteTransaction* trans,
+                         const BookmarkNode* node);
+
+  // Remove all the sync nodes associated with |node| and its children.
+  void RemoveSyncNodeHierarchy(const BookmarkNode* node);
+
+  bool running_;  // True if we have been told it is safe to process changes.
+  UnrecoverableErrorHandler* error_handler_;  // Guaranteed to outlive us.
+
+  // The two models we are processing changes between.  Non-NULL when
+  // |running_| is true.
+  BookmarkModel* bookmark_model_;
+  sync_api::UserShare* share_handle_;
+
+  // The two models should be associated according to this ModelAssociator.
+  scoped_refptr<ModelAssociator> model_associator_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChangeProcessor);
+};
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_GLUE_CHANGE_APPLICATOR_H_
+
+#endif  // CHROME_PERSONALIZATION
diff --git a/chrome/browser/sync/glue/model_associator.cc b/chrome/browser/sync/glue/model_associator.cc
index d4c4c45..47597ff 100644
--- a/chrome/browser/sync/glue/model_associator.cc
+++ b/chrome/browser/sync/glue/model_associator.cc
@@ -353,13 +353,15 @@ bool ModelAssociator::BuildAssocations() {
       if (child_node) {
         model->Move(child_node, parent_node, index);
         // Set the favicon for bookmark node from sync node or vice versa.
-        if (!sync_service_->SetBookmarkFavicon(&sync_child_node, child_node))
-          sync_service_->SetSyncNodeFavicon(child_node, &sync_child_node);
+        if (ChangeProcessor::SetBookmarkFavicon(&sync_child_node,
+            child_node, sync_service_->profile())) {
+          ChangeProcessor::SetSyncNodeFavicon(child_node, model,
+                                              &sync_child_node);
+        }
       } else {
         // Create a new bookmark node for the sync node.
-        child_node = sync_service_->CreateBookmarkNode(&sync_child_node,
-                                                       parent_node,
-                                                       index);
+        child_node = ChangeProcessor::CreateBookmarkNode(&sync_child_node,
+            parent_node, model, index);
       }
       AssociateIds(child_node->id(), sync_child_id);
       if (sync_child_node.GetIsFolder())
@@ -375,7 +377,8 @@ bool ModelAssociator::BuildAssocations() {
     // So the children starting from index in the parent bookmark node are the
     // ones that are not present in the parent sync node. So create them.
     for (int i = index; i < parent_node->GetChildCount(); ++i) {
-      sync_child_id = sync_service_->CreateSyncNode(parent_node, i, &trans);
+      sync_child_id = ChangeProcessor::CreateSyncNode(parent_node, model, i,
+          &trans, this, sync_service_);
       if (parent_node->GetChild(i)->is_folder())
         dfs_stack.push(sync_child_id);
     }
@@ -415,7 +418,7 @@ void ModelAssociator::PersistAssociations() {
     int64 sync_id = *iter;
     sync_api::WriteNode sync_node(&trans);
     if (!sync_node.InitByIdLookup(sync_id)) {
-      sync_service_->SetUnrecoverableError();
+      sync_service_->OnUnrecoverableError();
       return;
     }
     int64 node_id;
diff --git a/chrome/browser/sync/glue/model_associator.h b/chrome/browser/sync/glue/model_associator.h
index 9d5f825..a3b6e766e 100644
--- a/chrome/browser/sync/glue/model_associator.h
+++ b/chrome/browser/sync/glue/model_associator.h
@@ -28,6 +28,8 @@ class ProfileSyncService;
 
 namespace browser_sync {
 
+class ChangeProcessor;
+
 // Contains all model assocation related logic:
 // * Algorithm to associate bookmark model and sync model.
 // * Methods to get a bookmark node for a given sync node and vice versa.
diff --git a/chrome/browser/sync/glue/sync_backend_host.cc b/chrome/browser/sync/glue/sync_backend_host.cc
index ee75a79..14c8588 100644
--- a/chrome/browser/sync/glue/sync_backend_host.cc
+++ b/chrome/browser/sync/glue/sync_backend_host.cc
@@ -7,6 +7,7 @@
 #include "base/file_version_info.h"
 #include "base/file_util.h"
 #include "base/string_util.h"
+#include "chrome/browser/sync/glue/change_processor.h"
 #include "chrome/browser/sync/glue/sync_backend_host.h"
 #include "chrome/browser/sync/glue/http_bridge.h"
 #include "chrome/browser/sync/glue/bookmark_model_worker.h"
@@ -23,11 +24,13 @@ static const FilePath::CharType kSyncDataFolderName[] =
 namespace browser_sync {
 
 SyncBackendHost::SyncBackendHost(SyncFrontend* frontend,
-                                 const FilePath& profile_path)
+                                 const FilePath& profile_path,
+                                 ChangeProcessingInterface* processor)
     : core_thread_("Chrome_SyncCoreThread"),
       frontend_loop_(MessageLoop::current()),
       bookmark_model_worker_(NULL),
       frontend_(frontend),
+      processor_(processor),
       sync_data_folder_path_(profile_path.Append(kSyncDataFolderName)),
       last_auth_error_(AUTH_ERROR_NONE) {
   core_ = new Core(this);
@@ -250,7 +253,7 @@ void SyncBackendHost::Core::OnChangesApplied(
     DLOG(WARNING) << "Could not update bookmark model from non-UI thread";
     return;
   }
-  host_->frontend_->ApplyModelChanges(trans, changes, change_count);
+  host_->processor_->ApplyChangesFromSyncModel(trans, changes, change_count);
 }
 
 void SyncBackendHost::Core::OnSyncCycleCompleted() {
diff --git a/chrome/browser/sync/glue/sync_backend_host.h b/chrome/browser/sync/glue/sync_backend_host.h
index eb89e43..a15e1a7 100644
--- a/chrome/browser/sync/glue/sync_backend_host.h
+++ b/chrome/browser/sync/glue/sync_backend_host.h
@@ -22,7 +22,48 @@
 
 namespace browser_sync {
 
-class SyncFrontend;
+// SyncFrontend is the interface used by SyncBackendHost to communicate with
+// the entity that created it and, presumably, is interested in sync-related
+// activity.
+// NOTE: All methods will be invoked by a SyncBackendHost on the same thread
+// used to create that SyncBackendHost.
+class SyncFrontend {
+ public:
+  SyncFrontend() {}
+
+  // The backend has completed initialization and it is now ready to accept and
+  // process changes.
+  virtual void OnBackendInitialized() = 0;
+
+  // The backend queried the server recently and received some updates.
+  virtual void OnSyncCycleCompleted() = 0;
+
+  // The backend encountered an authentication problem and requests new
+  // credentials to be provided. See SyncBackendHost::Authenticate for details.
+  virtual void OnAuthError() = 0;
+
+ protected:
+  // Don't delete through SyncFrontend interface.
+  virtual ~SyncFrontend() {
+  }
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SyncFrontend);
+};
+
+// An interface used to apply changes from the sync model to the browser's
+// native model.  This does not currently distinguish between model data types.
+class ChangeProcessingInterface {
+ public:
+  // Changes have been applied to the backend model and are ready to be
+  // applied to the frontend model. See syncapi.h for detailed instructions on
+  // how to interpret and process |changes|.
+  virtual void ApplyChangesFromSyncModel(
+      const sync_api::BaseTransaction* trans,
+      const sync_api::SyncManager::ChangeRecord* changes,
+      int change_count) = 0;
+ protected:
+  virtual ~ChangeProcessingInterface() { }
+};
 
 // A UI-thread safe API into the sync backend that "hosts" the top-level
 // syncapi element, the SyncManager, on its own thread. This class handles
@@ -36,8 +77,10 @@ class SyncBackendHost {
 
   // Create a SyncBackendHost with a reference to the |frontend| that it serves
   // and communicates to via the SyncFrontend interface (on the same thread
-  // it used to call the constructor).
-  SyncBackendHost(SyncFrontend* frontend, const FilePath& proifle_path);
+  // it used to call the constructor), and push changes from sync_api through
+  // |processor|.
+  SyncBackendHost(SyncFrontend* frontend, const FilePath& profile_path,
+                  ChangeProcessingInterface* processor);
   ~SyncBackendHost();
 
   // Called on |frontend_loop_| to kick off asynchronous initialization.
@@ -222,6 +265,8 @@ class SyncBackendHost {
   // The frontend which we serve (and are owned by).
   SyncFrontend* frontend_;
 
+  ChangeProcessingInterface* processor_;  // Guaranteed to outlive us.
+
   // Path of the folder that stores the sync data files.
   FilePath sync_data_folder_path_;
 
@@ -231,43 +276,6 @@ class SyncBackendHost {
   DISALLOW_COPY_AND_ASSIGN(SyncBackendHost);
 };
 
-// SyncFrontend is the interface used by SyncBackendHost to communicate with
-// the entity that created it and, presumably, is interested in sync-related
-// activity.
-// NOTE: All methods will be invoked by a SyncBackendHost on the same thread
-// used to create that SyncBackendHost.
-class SyncFrontend {
- public:
-  typedef sync_api::BaseTransaction BaseTransaction;
-  typedef sync_api::SyncManager::ChangeRecord ChangeRecord;
-  SyncFrontend() {
-  }
-
-  // The backend has completed initialization and it is now ready to accept and
-  // process changes.
-  virtual void OnBackendInitialized() = 0;
-
-  // The backend queried the server recently and received some updates.
-  virtual void OnSyncCycleCompleted() = 0;
-
-  // The backend encountered an authentication problem and requests new
-  // credentials to be provided. See SyncBackendHost::Authenticate for details.
-  virtual void OnAuthError() = 0;
-
-  // Changes have been applied to the backend model and are ready to be
-  // applied to the frontend model. See syncapi.h for detailed instructions on
-  // how to interpret and process |changes|.
-  virtual void ApplyModelChanges(const BaseTransaction* trans,
-                                 const ChangeRecord* changes,
-                                 int change_count) = 0;
- protected:
-  // Don't delete through SyncFrontend interface.
-  virtual ~SyncFrontend() {
-  }
- private:
-  DISALLOW_COPY_AND_ASSIGN(SyncFrontend);
-};
-
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_SYNC_BACKEND_HOST_H_
diff --git a/chrome/browser/sync/profile_sync_service.cc b/chrome/browser/sync/profile_sync_service.cc
index 4de8f38..a426e53 100644
--- a/chrome/browser/sync/profile_sync_service.cc
+++ b/chrome/browser/sync/profile_sync_service.cc
@@ -25,11 +25,14 @@
 #include "chrome/browser/sync/personalization.h"
 #include "chrome/browser/sync/personalization_strings.h"
 #include "chrome/common/chrome_switches.h"
+#include "chrome/common/notification_service.h"
+#include "chrome/common/notification_type.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/pref_service.h"
 #include "chrome/common/time_format.h"
 #include "views/window/window.h"
 
+using browser_sync::ChangeProcessor;
 using browser_sync::ModelAssociator;
 using browser_sync::SyncBackendHost;
 
@@ -43,15 +46,21 @@ ProfileSyncService::ProfileSyncService(Profile* profile)
       backend_initialized_(false),
       expecting_first_run_auth_needed_event_(false),
       is_auth_in_progress_(false),
-      ready_to_process_changes_(false),
       unrecoverable_error_detected_(false),
       ALLOW_THIS_IN_INITIALIZER_LIST(wizard_(this)) {
+  change_processor_.reset(new ChangeProcessor(this));
 }
 
 ProfileSyncService::~ProfileSyncService() {
   Shutdown(false);
 }
 
+void ProfileSyncService::set_model_associator(
+    browser_sync::ModelAssociator* associator) {
+  model_associator_ = associator;
+  change_processor_->set_model_associator(associator);
+}
+
 void ProfileSyncService::Initialize() {
   InitSettings();
   RegisterPreferences();
@@ -108,15 +117,15 @@ void ProfileSyncService::StartUp() {
   last_synced_time_ = base::Time::FromInternalValue(
       profile_->GetPrefs()->GetInt64(prefs::kSyncLastSyncedTime));
 
-  backend_.reset(new SyncBackendHost(this, profile_->GetPath()));
+  backend_.reset(new SyncBackendHost(this, profile_->GetPath(),
+                                     change_processor_.get()));
 
-  // We add ourselves as an observer, and we remain one forever. Note we don't
-  // keep any pointer to the model, we just receive notifications from it.
-  BookmarkModel* model = profile_->GetBookmarkModel();
-  model->AddObserver(this);
+  registrar_.Add(this, NotificationType::BOOKMARK_MODEL_LOADED,
+                 Source<Profile>(profile_));
 
-  // Create new model assocation manager.
+  // Create new model assocation manager and change processor.
   model_associator_ = new ModelAssociator(this);
+  change_processor_->set_model_associator(model_associator_);
 
   // TODO(timsteele): HttpBridgeFactory should take a const* to the profile's
   // URLRequestContext, because it needs it to create HttpBridge objects, and
@@ -127,16 +136,15 @@ void ProfileSyncService::StartUp() {
 }
 
 void ProfileSyncService::Shutdown(bool sync_disabled) {
-  if (backend_.get()) {
+  registrar_.RemoveAll();
+
+  if (backend_.get())
     backend_->Shutdown(sync_disabled);
-    backend_.reset();
-  }
 
-  BookmarkModel* model = profile_->GetBookmarkModel();
-  if (model)
-    model->RemoveObserver(this);
+  change_processor_->Stop();
+  backend_.reset();
 
-  // Clear all assocations and throw away the assocation manager instance.
+  // Clear all associations and throw away the association manager instance.
   if (model_associator_.get()) {
     model_associator_->ClearAll();
     model_associator_ = NULL;
@@ -146,7 +154,6 @@ void ProfileSyncService::Shutdown(bool sync_disabled) {
   is_auth_in_progress_ = false;
   backend_initialized_ = false;
   expecting_first_run_auth_needed_event_ = false;
-  ready_to_process_changes_ = false;
   last_attempted_user_email_.clear();
 }
 
@@ -172,90 +179,14 @@ void ProfileSyncService::DisableForUser() {
   FOR_EACH_OBSERVER(Observer, observers_, OnStateChanged());
 }
 
-void ProfileSyncService::Loaded(BookmarkModel* model) {
+void ProfileSyncService::Observe(NotificationType type,
+                                 const NotificationSource& source,
+                                 const NotificationDetails& details) {
+  DCHECK_EQ(NotificationType::BOOKMARK_MODEL_LOADED, type.value);
+  registrar_.RemoveAll();
   StartProcessingChangesIfReady();
 }
 
-void ProfileSyncService::UpdateSyncNodeProperties(const BookmarkNode* src,
-                                                  sync_api::WriteNode* dst) {
-  // Set the properties of the item.
-  dst->SetIsFolder(src->is_folder());
-  dst->SetTitle(WideToUTF16(src->GetTitle()).c_str());
-  // URL is passed as a C string here because this interface avoids
-  // string16. SetURL copies the data into its own memory.
-  string16 url = UTF8ToUTF16(src->GetURL().spec());
-  dst->SetURL(url.c_str());
-  SetSyncNodeFavicon(src, dst);
-}
-
-void ProfileSyncService::EncodeFavicon(const BookmarkNode* src,
-                                       std::vector<unsigned char>* dst) const {
-  const SkBitmap& favicon = profile_->GetBookmarkModel()->GetFavIcon(src);
-
-  dst->clear();
-
-  // Check for zero-dimension images.  This can happen if the favicon is
-  // still being loaded.
-  if (favicon.empty())
-    return;
-
-  // Re-encode the BookmarkNode's favicon as a PNG, and pass the data to the
-  // sync subsystem.
-  if (!PNGEncoder::EncodeBGRASkBitmap(favicon, false, dst))
-    return;
-}
-
-void ProfileSyncService::RemoveOneSyncNode(sync_api::WriteTransaction* trans,
-                                           const BookmarkNode* node) {
-  sync_api::WriteNode sync_node(trans);
-  if (!model_associator_->InitSyncNodeFromBookmarkId(node->id(), &sync_node)) {
-    SetUnrecoverableError();
-    return;
-  }
-  // This node should have no children.
-  DCHECK(sync_node.GetFirstChildId() == sync_api::kInvalidId);
-  // Remove association and delete the sync node.
-  model_associator_->DisassociateIds(sync_node.GetId());
-  sync_node.Remove();
-}
-
-void ProfileSyncService::RemoveSyncNodeHierarchy(const BookmarkNode* topmost) {
-  sync_api::WriteTransaction trans(backend_->GetUserShareHandle());
-
-  // Later logic assumes that |topmost| has been unlinked.
-  DCHECK(!topmost->GetParent());
-
-  // A BookmarkModel deletion event means that |node| and all its children were
-  // deleted. Sync backend expects children to be deleted individually, so we do
-  // a depth-first-search here.  At each step, we consider the |index|-th child
-  // of |node|.  |index_stack| stores index values for the parent levels.
-  std::stack<int> index_stack;
-  index_stack.push(0);  // For the final pop.  It's never used.
-  const BookmarkNode* node = topmost;
-  int index = 0;
-  while (node) {
-    // The top of |index_stack| should always be |node|'s index.
-    DCHECK(!node->GetParent() || (node->GetParent()->IndexOfChild(node) ==
-      index_stack.top()));
-    if (index == node->GetChildCount()) {
-      // If we've processed all of |node|'s children, delete |node| and move
-      // on to its successor.
-      RemoveOneSyncNode(&trans, node);
-      node = node->GetParent();
-      index = index_stack.top() + 1;      // (top() + 0) was what we removed.
-      index_stack.pop();
-    } else {
-      // If |node| has an unprocessed child, process it next after pushing the
-      // current state onto the stack.
-      DCHECK_LT(index, node->GetChildCount());
-      index_stack.push(index);
-      node = node->GetChild(index);
-      index = 0;
-    }
-  }
-  DCHECK(index_stack.empty());  // Nothing should be left on the stack.
-}
-
 bool ProfileSyncService::MergeAndSyncAcceptanceNeeded() const {
   // If we've shown the dialog before, don't show it again.
   if (profile_->GetPrefs()->GetBoolean(prefs::kSyncHasSetupCompleted))
@@ -282,222 +213,14 @@ void ProfileSyncService::UpdateLastSyncedTime() {
   profile_->GetPrefs()->ScheduleSavePersistentPrefs();
 }
 
-void ProfileSyncService::BookmarkNodeAdded(BookmarkModel* model,
-                                           const BookmarkNode* parent,
-                                           int index) {
-  if (!ShouldPushChanges())
-    return;
-
-  DCHECK(backend_->GetUserShareHandle());
-
-  // Acquire a scoped write lock via a transaction.
-  sync_api::WriteTransaction trans(backend_->GetUserShareHandle());
-
-  CreateSyncNode(parent, index, &trans);
-}
-
-int64 ProfileSyncService::CreateSyncNode(const BookmarkNode* parent,
-                                         int index,
-                                         sync_api::WriteTransaction* trans) {
-  const BookmarkNode* child = parent->GetChild(index);
-  DCHECK(child);
-
-  // Create a WriteNode container to hold the new node.
-  sync_api::WriteNode sync_child(trans);
-
-  // Actually create the node with the appropriate initial position.
-  if (!PlaceSyncNode(CREATE, parent, index, trans, &sync_child)) {
-    LOG(WARNING) << "Sync node creation failed; recovery unlikely";
-    SetUnrecoverableError();
-    return sync_api::kInvalidId;
-  }
-
-  UpdateSyncNodeProperties(child, &sync_child);
-
-  // Associate the ID from the sync domain with the bookmark node, so that we
-  // can refer back to this item later.
-  model_associator_->AssociateIds(child->id(), sync_child.GetId());
-
-  return sync_child.GetId();
-}
-
-void ProfileSyncService::BookmarkNodeRemoved(BookmarkModel* model,
-                                             const BookmarkNode* parent,
-                                             int index,
-                                             const BookmarkNode* node) {
-  if (!ShouldPushChanges())
-    return;
-
-  RemoveSyncNodeHierarchy(node);
-}
-
-void ProfileSyncService::BookmarkNodeChanged(BookmarkModel* model,
-                                             const BookmarkNode* node) {
-  if (!ShouldPushChanges())
-    return;
-
-  // We shouldn't see changes to the top-level nodes.
-  DCHECK_NE(node, model->GetBookmarkBarNode());
-  DCHECK_NE(node, model->other_node());
-
-  // Acquire a scoped write lock via a transaction.
-  sync_api::WriteTransaction trans(backend_->GetUserShareHandle());
-
-  // Lookup the sync node that's associated with |node|.
-  sync_api::WriteNode sync_node(&trans);
-  if (!model_associator_->InitSyncNodeFromBookmarkId(node->id(), &sync_node)) {
-    SetUnrecoverableError();
-    return;
-  }
-
-  UpdateSyncNodeProperties(node, &sync_node);
-
-  DCHECK_EQ(sync_node.GetIsFolder(), node->is_folder());
-  DCHECK_EQ(model_associator_->GetBookmarkNodeFromSyncId(
-            sync_node.GetParentId()),
-            node->GetParent());
-  // This node's index should be one more than the predecessor's index.
-  DCHECK_EQ(node->GetParent()->IndexOfChild(node),
-            CalculateBookmarkModelInsertionIndex(node->GetParent(),
-                                                 &sync_node));
-}
-
-void ProfileSyncService::BookmarkNodeMoved(BookmarkModel* model,
-                                           const BookmarkNode* old_parent,
-                                           int old_index,
-                                           const BookmarkNode* new_parent,
-                                           int new_index) {
-  if (!ShouldPushChanges())
-    return;
-
-  const BookmarkNode* child = new_parent->GetChild(new_index);
-  // We shouldn't see changes to the top-level nodes.
-  DCHECK_NE(child, model->GetBookmarkBarNode());
-  DCHECK_NE(child, model->other_node());
-
-  // Acquire a scoped write lock via a transaction.
-  sync_api::WriteTransaction trans(backend_->GetUserShareHandle());
-
-  // Lookup the sync node that's associated with |child|.
-  sync_api::WriteNode sync_node(&trans);
-  if (!model_associator_->InitSyncNodeFromBookmarkId(child->id(),
-                                                     &sync_node)) {
-    SetUnrecoverableError();
-    return;
-  }
-
-  if (!PlaceSyncNode(MOVE, new_parent, new_index, &trans, &sync_node)) {
-    SetUnrecoverableError();
-    return;
-  }
-}
-
-void ProfileSyncService::BookmarkNodeFavIconLoaded(BookmarkModel* model,
-                                                   const BookmarkNode* node) {
-  BookmarkNodeChanged(model, node);
-}
-
-void ProfileSyncService::BookmarkNodeChildrenReordered(
-    BookmarkModel* model, const BookmarkNode* node) {
-  if (!ShouldPushChanges())
-    return;
-
-  // Acquire a scoped write lock via a transaction.
-  sync_api::WriteTransaction trans(backend_->GetUserShareHandle());
-
-  // The given node's children got reordered. We need to reorder all the
-  // children of the corresponding sync node.
-  for (int i = 0; i < node->GetChildCount(); ++i) {
-    sync_api::WriteNode sync_child(&trans);
-    if (!model_associator_->InitSyncNodeFromBookmarkId(node->GetChild(i)->id(),
-                                                       &sync_child)) {
-      SetUnrecoverableError();
-      return;
-    }
-    DCHECK_EQ(sync_child.GetParentId(),
-              model_associator_->GetSyncIdFromBookmarkId(node->id()));
-
-    if (!PlaceSyncNode(MOVE, node, i, &trans, &sync_child)) {
-      SetUnrecoverableError();
-      return;
-    }
-  }
-}
-
-bool ProfileSyncService::PlaceSyncNode(MoveOrCreate operation,
-                                       const BookmarkNode* parent,
-                                       int index,
-                                       sync_api::WriteTransaction* trans,
-                                       sync_api::WriteNode* dst) {
-  sync_api::ReadNode sync_parent(trans);
-  if (!model_associator_->InitSyncNodeFromBookmarkId(parent->id(),
-                                                     &sync_parent)) {
-    LOG(WARNING) << "Parent lookup failed";
-    SetUnrecoverableError();
-    return false;
-  }
-
-  bool success = false;
-  if (index == 0) {
-    // Insert into first position.
-    success = (operation == CREATE) ? dst->InitByCreation(sync_parent, NULL) :
-                                      dst->SetPosition(sync_parent, NULL);
-    if (success) {
-      DCHECK_EQ(dst->GetParentId(), sync_parent.GetId());
-      DCHECK_EQ(dst->GetId(), sync_parent.GetFirstChildId());
-      DCHECK_EQ(dst->GetPredecessorId(), sync_api::kInvalidId);
-    }
-  } else {
-    // Find the bookmark model predecessor, and insert after it.
-    const BookmarkNode* prev = parent->GetChild(index - 1);
-    sync_api::ReadNode sync_prev(trans);
-    if (!model_associator_->InitSyncNodeFromBookmarkId(prev->id(),
-                                                       &sync_prev)) {
-      LOG(WARNING) << "Predecessor lookup failed";
-      return false;
-    }
-    success = (operation == CREATE) ?
-        dst->InitByCreation(sync_parent, &sync_prev) :
-        dst->SetPosition(sync_parent, &sync_prev);
-    if (success) {
-      DCHECK_EQ(dst->GetParentId(), sync_parent.GetId());
-      DCHECK_EQ(dst->GetPredecessorId(), sync_prev.GetId());
-      DCHECK_EQ(dst->GetId(), sync_prev.GetSuccessorId());
-    }
-  }
-  return success;
-}
-
 // An invariant has been violated.  Transition to an error state where we try
 // to do as little work as possible, to avoid further corruption or crashes.
-void ProfileSyncService::SetUnrecoverableError() {
+void ProfileSyncService::OnUnrecoverableError() {
   unrecoverable_error_detected_ = true;
+  change_processor_->Stop();
   LOG(ERROR) << "Unrecoverable error detected -- ProfileSyncService unusable.";
 }
 
-// Determine the bookmark model index to which a node must be moved so that
-// predecessor of the node (in the bookmark model) matches the predecessor of
-// |source| (in the sync model).
-// As a precondition, this assumes that the predecessor of |source| has been
-// updated and is already in the correct position in the bookmark model.
-int ProfileSyncService::CalculateBookmarkModelInsertionIndex(
-    const BookmarkNode* parent,
-    const sync_api::BaseNode* child_info) const {
-  DCHECK(parent);
-  DCHECK(child_info);
-  int64 predecessor_id = child_info->GetPredecessorId();
-  // A return ID of kInvalidId indicates no predecessor.
-  if (predecessor_id == sync_api::kInvalidId)
-    return 0;
-
-  // Otherwise, insert after the predecessor bookmark node.
-  const BookmarkNode* predecessor =
-      model_associator_->GetBookmarkNodeFromSyncId(predecessor_id);
-  DCHECK(predecessor);
-  DCHECK_EQ(predecessor->GetParent(), parent);
-  return parent->IndexOfChild(predecessor) + 1;
-}
-
 void ProfileSyncService::OnBackendInitialized() {
   backend_initialized_ = true;
   StartProcessingChangesIfReady();
@@ -553,206 +276,6 @@ void ProfileSyncService::ShowLoginDialog() {
     wizard_.Step(SyncSetupWizard::GAIA_LOGIN);
 }
 
-// ApplyModelChanges is called by the sync backend after changes have been made
-// to the sync engine's model.  Apply these changes to the browser bookmark
-// model.
-void ProfileSyncService::ApplyModelChanges(
-    const sync_api::BaseTransaction* trans,
-    const sync_api::SyncManager::ChangeRecord* changes,
-    int change_count) {
-  if (!ShouldPushChanges())
-    return;
-
-  // A note about ordering.  Sync backend is responsible for ordering the change
-  // records in the following order:
-  //
-  // 1. Deletions, from leaves up to parents.
-  // 2. Existing items with synced parents & predecessors.
-  // 3. New items with synced parents & predecessors.
-  // 4. Items with parents & predecessors in the list.
-  // 5. Repeat #4 until all items are in the list.
-  //
-  // "Predecessor" here means the previous item within a given folder; an item
-  // in the first position is always said to have a synced predecessor.
-  // For the most part, applying these changes in the order given will yield
-  // the correct result.  There is one exception, however: for items that are
-  // moved away from a folder that is being deleted, we will process the delete
-  // before the move.  Since deletions in the bookmark model propagate from
-  // parent to child, we must move them to a temporary location.
-  BookmarkModel* model = profile_->GetBookmarkModel();
-
-  // We are going to make changes to the bookmarks model, but don't want to end
-  // up in a feedback loop, so remove ourselves as an observer while applying
-  // changes.
-  model->RemoveObserver(this);
-
-  // A parent to hold nodes temporarily orphaned by parent deletion.  It is
-  // lazily created inside the loop.
-  const BookmarkNode* foster_parent = NULL;
-  for (int i = 0; i < change_count; ++i) {
-    const BookmarkNode* dst =
-        model_associator_->GetBookmarkNodeFromSyncId(changes[i].id);
-    // Ignore changes to the permanent top-level nodes.  We only care about
-    // their children.
-    if ((dst == model->GetBookmarkBarNode()) || (dst == model->other_node()))
-      continue;
-    if (changes[i].action ==
-        sync_api::SyncManager::ChangeRecord::ACTION_DELETE) {
-      // Deletions should always be at the front of the list.
-      DCHECK(i == 0 || changes[i-1].action == changes[i].action);
-      // Children of a deleted node should not be deleted; they may be
-      // reparented by a later change record.  Move them to a temporary place.
-      DCHECK(dst) << "Could not find node to be deleted";
-      const BookmarkNode* parent = dst->GetParent();
-      if (dst->GetChildCount()) {
-        if (!foster_parent) {
-          foster_parent = model->AddGroup(model->other_node(),
-                                          model->other_node()->GetChildCount(),
-                                          std::wstring());
-        }
-        for (int i = dst->GetChildCount() - 1; i >= 0; --i) {
-          model->Move(dst->GetChild(i), foster_parent,
-                      foster_parent->GetChildCount());
-        }
-      }
-      DCHECK_EQ(dst->GetChildCount(), 0) << "Node being deleted has children";
-      model->Remove(parent, parent->IndexOfChild(dst));
-      dst = NULL;
-      model_associator_->DisassociateIds(changes[i].id);
-    } else {
-      DCHECK_EQ((changes[i].action ==
-          sync_api::SyncManager::ChangeRecord::ACTION_ADD), (dst == NULL))
-          << "ACTION_ADD should be seen if and only if the node is unknown.";
-
-      sync_api::ReadNode src(trans);
-      if (!src.InitByIdLookup(changes[i].id)) {
-        LOG(ERROR) << "ApplyModelChanges was passed a bad ID";
-        SetUnrecoverableError();
-        return;
-      }
-
-      CreateOrUpdateBookmarkNode(&src, model);
-    }
-  }
-  // Clean up the temporary node.
-  if (foster_parent) {
-    // There should be no nodes left under the foster parent.
-    DCHECK_EQ(foster_parent->GetChildCount(), 0);
-    model->Remove(foster_parent->GetParent(),
-                  foster_parent->GetParent()->IndexOfChild(foster_parent));
-    foster_parent = NULL;
-  }
-
-  // We are now ready to hear about bookmarks changes again.
-  model->AddObserver(this);
-}
-
-// Create a bookmark node corresponding to |src| if one is not already
-// associated with |src|.
-const BookmarkNode* ProfileSyncService::CreateOrUpdateBookmarkNode(
-    sync_api::BaseNode* src,
-    BookmarkModel* model) {
-  const BookmarkNode* parent =
-      model_associator_->GetBookmarkNodeFromSyncId(src->GetParentId());
-  if (!parent) {
-    DLOG(WARNING) << "Could not find parent of node being added/updated."
-      << " Node title: " << src->GetTitle()
-      << ", parent id = " << src->GetParentId();
-    return NULL;
-  }
-  int index = CalculateBookmarkModelInsertionIndex(parent, src);
-  const BookmarkNode* dst = model_associator_->GetBookmarkNodeFromSyncId(
-      src->GetId());
-  if (!dst) {
-    dst = CreateBookmarkNode(src, parent, index);
-    model_associator_->AssociateIds(dst->id(), src->GetId());
-  } else {
-    // URL and is_folder are not expected to change.
-    // TODO(ncarter): Determine if such changes should be legal or not.
-    DCHECK_EQ(src->GetIsFolder(), dst->is_folder());
-
-    // Handle reparenting and/or repositioning.
-    model->Move(dst, parent, index);
-
-    // Handle title update and URL changes due to possible conflict resolution
-    // that can happen if both a local user change and server change occur
-    // within a sufficiently small time interval.
-    const BookmarkNode* old_dst = dst;
-    dst = bookmark_utils::ApplyEditsWithNoGroupChange(model, parent, dst,
-        UTF16ToWide(src->GetTitle()),
-        src->GetIsFolder() ? GURL() : GURL(src->GetURL()),
-        NULL);  // NULL because we don't need a BookmarkEditor::Handler.
-    if (dst != old_dst) {  // dst was replaced with a new node with new URL.
-      model_associator_->DisassociateIds(src->GetId());
-      model_associator_->AssociateIds(dst->id(), src->GetId());
-    }
-    SetBookmarkFavicon(src, dst);
-  }
-
-  return dst;
-}
-
-// Creates a bookmark node under the given parent node from the given sync
-// node. Returns the newly created node.
-const BookmarkNode* ProfileSyncService::CreateBookmarkNode(
-    sync_api::BaseNode* sync_node,
-    const BookmarkNode* parent,
-    int index) const {
-  DCHECK(parent);
-  DCHECK(index >= 0 && index <= parent->GetChildCount());
-  BookmarkModel* model = profile_->GetBookmarkModel();
-
-  const BookmarkNode* node;
-  if (sync_node->GetIsFolder()) {
-    node = model->AddGroup(parent, index, UTF16ToWide(sync_node->GetTitle()));
-  } else {
-    GURL url(sync_node->GetURL());
-    node = model->AddURL(parent, index,
-                         UTF16ToWide(sync_node->GetTitle()), url);
-    SetBookmarkFavicon(sync_node, node);
-  }
-  return node;
-}
-
-// Sets the favicon of the given bookmark node from the given sync node.
-bool ProfileSyncService::SetBookmarkFavicon(
-    sync_api::BaseNode* sync_node,
-    const BookmarkNode* bookmark_node) const {
-  size_t icon_size = 0;
-  const unsigned char* icon_bytes = sync_node->GetFaviconBytes(&icon_size);
-  if (!icon_size || !icon_bytes)
-    return false;
-
-  // Registering a favicon requires that we provide a source URL, but we
-  // don't know where these came from.  Currently we just use the
-  // destination URL, which is not correct, but since the favicon URL
-  // is used as a key in the history's thumbnail DB, this gives us a value
-  // which does not collide with others.
-  GURL fake_icon_url = bookmark_node->GetURL();
-
-  std::vector<unsigned char> icon_bytes_vector(icon_bytes,
-                                               icon_bytes + icon_size);
-
-  HistoryService* history =
-      profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
-
-  history->AddPage(bookmark_node->GetURL());
-  history->SetFavIcon(bookmark_node->GetURL(),
-                      fake_icon_url,
-                      icon_bytes_vector);
-
-  return true;
-}
-
-void ProfileSyncService::SetSyncNodeFavicon(
-    const BookmarkNode* bookmark_node,
-    sync_api::WriteNode* sync_node) const {
-  std::vector<unsigned char> favicon_bytes;
-  EncodeFavicon(bookmark_node, &favicon_bytes);
-  if (!favicon_bytes.empty())
-    sync_node->SetFaviconBytes(&favicon_bytes[0], favicon_bytes.size());
-}
-
 SyncBackendHost::StatusSummary ProfileSyncService::QuerySyncStatusSummary() {
   return backend_->GetStatusSummary();
 }
@@ -821,11 +344,12 @@ void ProfileSyncService::OnUserAcceptedMergeAndSync() {
   wizard_.Step(SyncSetupWizard::DONE);  // TODO(timsteele): error state?
   if (!merge_success) {
     LOG(ERROR) << "Model assocation failed.";
-    SetUnrecoverableError();
+    OnUnrecoverableError();
     return;
   }
 
-  ready_to_process_changes_ = true;
+  change_processor_->Start(profile_->GetBookmarkModel(),
+                           backend_->GetUserShareHandle());
   FOR_EACH_OBSERVER(Observer, observers_, OnStateChanged());
 }
 
@@ -842,7 +366,7 @@ void ProfileSyncService::OnUserCancelledDialog() {
 void ProfileSyncService::StartProcessingChangesIfReady() {
   BookmarkModel* model = profile_->GetBookmarkModel();
 
-  DCHECK(!ready_to_process_changes_);
+  DCHECK(!change_processor_->IsRunning());
 
   // First check if the subsystems are ready.  We can't proceed until they
   // both have finished loading.
@@ -867,11 +391,12 @@ void ProfileSyncService::StartProcessingChangesIfReady() {
   wizard_.Step(SyncSetupWizard::DONE);  // TODO(timsteele): error state?
   if (!merge_success) {
     LOG(ERROR) << "Model assocation failed.";
-    SetUnrecoverableError();
+    OnUnrecoverableError();
     return;
   }
 
-  ready_to_process_changes_ = true;
+  change_processor_->Start(profile_->GetBookmarkModel(),
+                           backend_->GetUserShareHandle());
   FOR_EACH_OBSERVER(Observer, observers_, OnStateChanged());
 }
 
@@ -892,8 +417,10 @@ void ProfileSyncService::SyncEvent(SyncEventCodes code) {
 }
 
 bool ProfileSyncService::ShouldPushChanges() {
-  return ready_to_process_changes_ &&     // Wait for model load and merge.
-         !unrecoverable_error_detected_;  // Halt after any terrible events.
+  // True only after all bootstrapping has succeeded: the bookmark model is
+  // loaded, the sync backend is initialized, the two domains are
+  // consistent with one another, and no unrecoverable error has transpired.
+  return change_processor_->IsRunning();
 }
 
 #endif  // CHROME_PERSONALIZATION
diff --git a/chrome/browser/sync/profile_sync_service.h b/chrome/browser/sync/profile_sync_service.h
index a2f956b..ae2047e 100644
--- a/chrome/browser/sync/profile_sync_service.h
+++ b/chrome/browser/sync/profile_sync_service.h
@@ -17,9 +17,11 @@
 #include "base/scoped_ptr.h"
 #include "chrome/browser/bookmarks/bookmark_model.h"
 #include "chrome/browser/profile.h"
+#include "chrome/browser/sync/glue/change_processor.h"
 #include "chrome/browser/sync/glue/model_associator.h"
 #include "chrome/browser/sync/glue/sync_backend_host.h"
 #include "chrome/browser/views/sync/sync_setup_wizard.h"
+#include "chrome/common/notification_registrar.h"
 #include "googleurl/src/gurl.h"
 
 class CommandLine;
@@ -28,6 +30,18 @@ class Profile;
 
 namespace browser_sync {
 class ModelAssociator;
+
+class UnrecoverableErrorHandler {
+ public:
+  // Call this when normal operation detects that the bookmark model and the
+  // syncer model are inconsistent, or similar.  The ProfileSyncService will
+  // try to avoid doing any work to avoid crashing or corrupting things
+  // further, and will report an error status if queried.
+  virtual void OnUnrecoverableError() = 0;
+ protected:
+  virtual ~UnrecoverableErrorHandler() { }
+};
+
 }
 
 // Various UI components such as the New Tab page can be driven by observing
@@ -47,8 +61,9 @@ class ProfileSyncServiceObserver {
 
 // ProfileSyncService is the layer between browser subsystems like bookmarks,
 // and the sync backend.
-class ProfileSyncService : public BookmarkModelObserver,
-                           public browser_sync::SyncFrontend {
+class ProfileSyncService : public NotificationObserver,
+                           public browser_sync::SyncFrontend,
+                           public browser_sync::UnrecoverableErrorHandler {
  public:
   typedef ProfileSyncServiceObserver Observer;
   typedef browser_sync::SyncBackendHost::Status Status;
@@ -91,36 +106,15 @@ class ProfileSyncService : public BookmarkModelObserver,
   bool HasSyncSetupCompleted() const;
   void SetSyncSetupCompleted();
 
-  // BookmarkModelObserver implementation.
-  virtual void Loaded(BookmarkModel* model);
-  virtual void BookmarkModelBeingDeleted(BookmarkModel* model) {}
-  virtual void BookmarkNodeMoved(BookmarkModel* model,
-                                 const BookmarkNode* old_parent,
-                                 int old_index,
-                                 const BookmarkNode* new_parent,
-                                 int new_index);
-  virtual void BookmarkNodeAdded(BookmarkModel* model,
-                                 const BookmarkNode* parent,
-                                 int index);
-  virtual void BookmarkNodeRemoved(BookmarkModel* model,
-                                   const BookmarkNode* parent,
-                                   int index,
-                                   const BookmarkNode* node);
-  virtual void BookmarkNodeChanged(BookmarkModel* model,
-                                   const BookmarkNode* node);
-  virtual void BookmarkNodeFavIconLoaded(BookmarkModel* model,
-                                         const BookmarkNode* node);
-  virtual void BookmarkNodeChildrenReordered(BookmarkModel* model,
-                                             const BookmarkNode* node);
+  // NotificationObserver implementation.
+  virtual void ProfileSyncService::Observe(NotificationType type,
+                                           const NotificationSource& source,
+                                           const NotificationDetails& details);
 
   // SyncFrontend implementation.
   virtual void OnBackendInitialized();
   virtual void OnSyncCycleCompleted();
   virtual void OnAuthError();
-  virtual void ApplyModelChanges(
-      const sync_api::BaseTransaction* trans,
-      const sync_api::SyncManager::ChangeRecord* changes,
-      int change_count);
 
   // Called when a user enters credentials through UI.
   virtual void OnUserSubmittedAuth(const std::string& username,
@@ -196,6 +190,11 @@ class ProfileSyncService : public BookmarkModelObserver,
   // Record stats on various events.
   static void SyncEvent(SyncEventCodes code);
 
+  // UnrecoverableErrorHandler implementation.
+  virtual void OnUnrecoverableError();
+
+  browser_sync::SyncBackendHost* backend() { return backend_.get(); }
+
  protected:
   // Call this after any of the subsystems being synced (the bookmark
   // model and the sync backend) finishes its initialization.  When everything
@@ -203,15 +202,6 @@ class ProfileSyncService : public BookmarkModelObserver,
   // initially in sync, and start forwarding changes between the two models.
   void StartProcessingChangesIfReady();
 
-  // Various member accessors needed by unit tests.
-  browser_sync::SyncBackendHost* backend() { return backend_.get(); }
-
-  // Call this when normal operation detects that the bookmark model and the
-  // syncer model are inconsistent, or similar.  The ProfileSyncService will
-  // try to avoid doing any work to avoid crashing or corrupting things
-  // further, and will report an error status if queried.
-  void SetUnrecoverableError();
-
   // Returns whether processing changes is allowed.  Check this before doing
   // any model-modifying operations.
   bool ShouldPushChanges();
@@ -230,9 +220,7 @@ class ProfileSyncService : public BookmarkModelObserver,
   virtual void InitializeBackend();
 
   // Tests need this.
-  void set_model_associator(browser_sync::ModelAssociator* manager) {
-    model_associator_ = manager;
-  }
+  void set_model_associator(browser_sync::ModelAssociator* associator);
 
   // We keep track of the last auth error observed so we can cover up the first
   // "expected" auth failure from observers.
@@ -244,90 +232,14 @@ class ProfileSyncService : public BookmarkModelObserver,
   std::string last_attempted_user_email_;
 
  private:
-  friend class browser_sync::ModelAssociator;
   friend class ProfileSyncServiceTest;
   friend class ProfileSyncServiceTestHarness;
   friend class TestModelAssociator;
   FRIEND_TEST(ProfileSyncServiceTest, UnrecoverableErrorSuspendsService);
 
-  enum MoveOrCreate {
-    MOVE,
-    CREATE,
-  };
-
   // Initializes the various settings from the command line.
   void InitSettings();
 
-  // Treat the |index|th child of |parent| as a newly added node, and create a
-  // corresponding node in the sync domain using |trans|.  All properties
-  // will be transferred to the new node.  A node corresponding to |parent|
-  // must already exist and be associated for this call to succeed.  Returns
-  // the ID of the just-created node, or if creation fails, kInvalidID.
-  int64 CreateSyncNode(const BookmarkNode* parent,
-                       int index,
-                       sync_api::WriteTransaction* trans);
-
-  // Create a bookmark node corresponding to |src| if one is not already
-  // associated with |src|.  Returns the node that was created or updated.
-  const BookmarkNode* CreateOrUpdateBookmarkNode(
-      sync_api::BaseNode* src,
-      BookmarkModel* model);
-
-  // Creates a bookmark node under the given parent node from the given sync
-  // node. Returns the newly created node.
-  const BookmarkNode* CreateBookmarkNode(
-      sync_api::BaseNode* sync_node,
-      const BookmarkNode* parent,
-      int index) const;
-
-  // Sets the favicon of the given bookmark node from the given sync node.
-  // Returns whether the favicon was set in the bookmark node.
-  bool SetBookmarkFavicon(sync_api::BaseNode* sync_node,
-                          const BookmarkNode* bookmark_node) const;
-
-  // Sets the favicon of the given sync node from the given bookmark node.
-  void SetSyncNodeFavicon(const BookmarkNode* bookmark_node,
-                          sync_api::WriteNode* sync_node) const;
-
-  // Helper function to determine the appropriate insertion index of sync node
-  // |node| under the Bookmark model node |parent|, to make the positions
-  // match up between the two models. This presumes that the predecessor of the
-  // item (in the bookmark model) has already been moved into its appropriate
-  // position.
-  int CalculateBookmarkModelInsertionIndex(
-      const BookmarkNode* parent,
-      const sync_api::BaseNode* node) const;
-
-  // Helper function used to fix the position of a sync node so that it matches
-  // the position of a corresponding bookmark model node. |parent| and
-  // |index| identify the bookmark model position.  |dst| is the node whose
-  // position is to be fixed.  If |operation| is CREATE, treat |dst| as an
-  // uncreated node and set its position via InitByCreation(); otherwise,
-  // |dst| is treated as an existing node, and its position will be set via
-  // SetPosition().  |trans| is the transaction to which |dst| belongs. Returns
-  // false on failure.
-  bool PlaceSyncNode(MoveOrCreate operation,
-                     const BookmarkNode* parent,
-                     int index,
-                     sync_api::WriteTransaction* trans,
-                     sync_api::WriteNode* dst);
-
-  // Copy properties (but not position) from |src| to |dst|.
-  void UpdateSyncNodeProperties(const BookmarkNode* src,
-                                sync_api::WriteNode* dst);
-
-  // Helper function to encode a bookmark's favicon into a PNG byte vector.
-  void EncodeFavicon(const BookmarkNode* src,
-                     std::vector<unsigned char>* dst) const;
-
-  // Remove the sync node corresponding to |node|.  It shouldn't have
-  // any children.
-  void RemoveOneSyncNode(sync_api::WriteTransaction* trans,
-                         const BookmarkNode* node);
-
-  // Remove all the sync nodes associated with |node| and its children.
-  void RemoveSyncNodeHierarchy(const BookmarkNode* node);
-
   // Whether the sync merge warning should be shown.
   bool MergeAndSyncAcceptanceNeeded() const;
 
@@ -355,6 +267,10 @@ class ProfileSyncService : public BookmarkModelObserver,
   // other threads.
   scoped_ptr<browser_sync::SyncBackendHost> backend_;
 
+  scoped_ptr<browser_sync::ChangeProcessor> change_processor_;
+
+  NotificationRegistrar registrar_;
+
   // Whether the SyncBackendHost has been initialized.
   bool backend_initialized_;
 
@@ -375,11 +291,6 @@ class ProfileSyncService : public BookmarkModelObserver,
   // As its name suggests, this should NOT be used for anything other than UI.
   bool is_auth_in_progress_;
 
-  // True only after all bootstrapping has succeeded: the bookmark model is
-  // loaded, the sync backend is initialized, and the two domains are
-  // consistent with one another.
-  bool ready_to_process_changes_;
-
   // True if an unrecoverable error (e.g. violation of an assumed invariant)
   // occurred during syncer operation.  This value should be checked before
   // doing any work that might corrupt things further.
diff --git a/chrome/browser/sync/profile_sync_service_unittest.cc b/chrome/browser/sync/profile_sync_service_unittest.cc
index ef12916..b2062b5 100644
--- a/chrome/browser/sync/profile_sync_service_unittest.cc
+++ b/chrome/browser/sync/profile_sync_service_unittest.cc
@@ -16,11 +16,13 @@
 #include "chrome/browser/profile.h"
 #include "chrome/browser/sync/engine/syncapi.h"
 #include "chrome/browser/sync/glue/model_associator.h"
+#include "chrome/browser/sync/glue/sync_backend_host.h"
 #include "chrome/browser/sync/profile_sync_service.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/test/testing_profile.h"
 
 using std::vector;
+using browser_sync::ChangeProcessingInterface;
 using browser_sync::ModelAssociator;
 using browser_sync::SyncBackendHost;
 
@@ -222,9 +224,9 @@ class FakeServerChange {
   }
 
   // Pass the fake change list to |service|.
-  void ApplyPendingChanges(ProfileSyncService* service) {
-    service->ApplyModelChanges(trans_, changes_.size() ? &changes_[0] : NULL,
-                               changes_.size());
+  void ApplyPendingChanges(browser_sync::ChangeProcessingInterface* processor) {
+    processor->ApplyChangesFromSyncModel(trans_,
+        changes_.size() ? &changes_[0] : NULL, changes_.size());
   }
 
   const vector<sync_api::SyncManager::ChangeRecord>& changes() {
@@ -272,6 +274,11 @@ class ProfileSyncServiceTest : public testing::Test {
     return service_->model_associator_;
   }
 
+  ChangeProcessingInterface* change_processor() {
+    DCHECK(service_.get());
+    return service_->change_processor_.get();
+  }
+
   void StartSyncService() {
     if (!service_.get()) {
       service_.reset(new TestProfileSyncService(profile_.get()));
@@ -539,7 +546,7 @@ TEST_F(ProfileSyncServiceTest, ServerChangeProcessing) {
   for (it = adds.changes().begin(); it != adds.changes().end(); ++it)
     ExpectBrowserNodeUnknown(it->id);
 
-  adds.ApplyPendingChanges(service_.get());
+  adds.ApplyPendingChanges(change_processor());
 
   // Make sure the bookmark model received all of the nodes in |adds|.
   for (it = adds.changes().begin(); it != adds.changes().end(); ++it)
@@ -572,7 +579,7 @@ TEST_F(ProfileSyncServiceTest, ServerChangeProcessing) {
   ExpectBrowserNodeParent(u3, u3_old_parent);
 
   // Apply the changes.
-  mods.ApplyPendingChanges(service_.get());
+  mods.ApplyPendingChanges(change_processor());
 
   // Check for successful application.
   for (it = mods.changes().begin(); it != mods.changes().end(); ++it)
@@ -587,7 +594,7 @@ TEST_F(ProfileSyncServiceTest, ServerChangeProcessing) {
   ExpectBrowserNodeKnown(u2);
   ExpectBrowserNodeKnown(u3);
 
-  dels.ApplyPendingChanges(service_.get());
+  dels.ApplyPendingChanges(change_processor());
 
   ExpectBrowserNodeUnknown(u2);
   ExpectBrowserNodeUnknown(u3);
@@ -622,7 +629,7 @@ TEST_F(ProfileSyncServiceTest, ServerChangeRequiringFosterParent) {
   for (it = adds.changes().begin(); it != adds.changes().end(); ++it)
     ExpectBrowserNodeUnknown(it->id);
 
-  adds.ApplyPendingChanges(service_.get());
+  adds.ApplyPendingChanges(change_processor());
 
   // Make sure the bookmark model received all of the nodes in |adds|.
   for (it = adds.changes().begin(); it != adds.changes().end(); ++it)
@@ -640,7 +647,7 @@ TEST_F(ProfileSyncServiceTest, ServerChangeRequiringFosterParent) {
   ops.ModifyPosition(u5, f6, 0);
   ops.Delete(f1);
 
-  ops.ApplyPendingChanges(service_.get());
+  ops.ApplyPendingChanges(change_processor());
 
   ExpectModelMatch(&trans);
 }
@@ -658,7 +665,7 @@ TEST_F(ProfileSyncServiceTest, ServerChangeWithNonCanonicalURL) {
     EXPECT_NE(GURL(url).spec(), url);
     int64 u1 = adds.AddURL(L"u1", UTF8ToWide(url), other_bookmarks_id(), 0);
 
-    adds.ApplyPendingChanges(service_.get());
+    adds.ApplyPendingChanges(change_processor());
 
     EXPECT_TRUE(model_->other_node()->GetChildCount() == 1);
     ExpectModelMatch(&trans);
@@ -688,7 +695,7 @@ TEST_F(ProfileSyncServiceTest, DISABLED_ServerChangeWithInvalidURL) {
     EXPECT_FALSE(GURL("x").is_valid());
     int64 u1 = adds.AddURL(L"u1", L"x", other_bookmarks_id(), 0);
 
-    adds.ApplyPendingChanges(service_.get());
+    adds.ApplyPendingChanges(change_processor());
 
     // We're lenient about what should happen -- the model could wind up with
     // the node or without it; but things should be consistent, and we
diff --git a/chrome/chrome.gyp b/chrome/chrome.gyp
index be29b86..3a924ad 100644
--- a/chrome/chrome.gyp
+++ b/chrome/chrome.gyp
@@ -1685,6 +1685,8 @@
         'browser/sync/engine/syncapi.h',
         'browser/sync/glue/bookmark_model_worker.cc',
         'browser/sync/glue/bookmark_model_worker.h',
+        'browser/sync/glue/change_processor.cc',
+        'browser/sync/glue/change_processor.h',
         'browser/sync/glue/http_bridge.cc',
         'browser/sync/glue/http_bridge.h',
         'browser/sync/glue/model_associator.cc',
diff --git a/chrome/test/live_sync/profile_sync_service_test_harness.cc b/chrome/test/live_sync/profile_sync_service_test_harness.cc
index debb782..61c8deb 100644
--- a/chrome/test/live_sync/profile_sync_service_test_harness.cc
+++ b/chrome/test/live_sync/profile_sync_service_test_harness.cc
@@ -145,7 +145,7 @@ bool ProfileSyncServiceTestHarness::RunStateChangeMachine() {
       SignalStateCompleteWithNextState(WAITING_FOR_READY_TO_PROCESS_CHANGES);
       break;
     case WAITING_FOR_READY_TO_PROCESS_CHANGES:
-      if (service_->ready_to_process_changes_) {
+      if (service_->ShouldPushChanges()) {
         SignalStateCompleteWithNextState(WAITING_FOR_NOTHING);
       }
       break;