Add return values to SyncerCommand

This is part 1 of 3 in a series of patches to remove the unnecessary
SYNC_CYCLE_CONTINUATION sync cycle that follows every sync commit.

In this patch, we add a return value to all SyncerCommands.  This will
make it easier for us to tell when a command has failed, and why.

Currently, the error detection does not work very well.  We don't have
much support for errors that occur on worker threads.  Many commands will
return an error only in case of directory lookup failure, but return
NO_ERROR otherwise.

This is OK because we're not aiming to fully implement error detection
in this commit.  This provides a base we can build on in future commits.

BUG=94670,109422
TEST=


Review URL: http://codereview.chromium.org/9113024

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@116963 0039d316-1c4b-4281-b951-d872f2087c98

50 files changed, 308 insertions, 188 deletions

diff --git a/chrome/browser/sync/engine/apply_updates_command.cc b/chrome/browser/sync/engine/apply_updates_command.cc
index 70ff143..f5c3cef 100644
--- a/chrome/browser/sync/engine/apply_updates_command.cc
+++ b/chrome/browser/sync/engine/apply_updates_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -44,12 +44,13 @@ std::set<ModelSafeGroup> ApplyUpdatesCommand::GetGroupsToChange(
   return groups_with_unapplied_updates;
 }
 
-void ApplyUpdatesCommand::ModelChangingExecuteImpl(SyncSession* session) {
+SyncerError ApplyUpdatesCommand::ModelChangingExecuteImpl(
+    SyncSession* session) {
   syncable::ScopedDirLookup dir(session->context()->directory_manager(),
                                 session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   }
 
   syncable::WriteTransaction trans(FROM_HERE, syncable::SYNCER, dir);
@@ -91,6 +92,8 @@ void ApplyUpdatesCommand::ModelChangingExecuteImpl(SyncSession* session) {
       dir->set_initial_sync_ended_for_type(it.Get(), true);
     }
   }
+
+  return SYNCER_OK;
 }
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/engine/apply_updates_command.h b/chrome/browser/sync/engine/apply_updates_command.h
index d75754f..fc7a42c 100644
--- a/chrome/browser/sync/engine/apply_updates_command.h
+++ b/chrome/browser/sync/engine/apply_updates_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -20,7 +20,7 @@ class ApplyUpdatesCommand : public ModelChangingSyncerCommand {
   // ModelChangingSyncerCommand implementation.
   virtual std::set<ModelSafeGroup> GetGroupsToChange(
       const sessions::SyncSession& session) const OVERRIDE;
-  virtual void ModelChangingExecuteImpl(
+  virtual SyncerError ModelChangingExecuteImpl(
       sessions::SyncSession* session) OVERRIDE;
 
  private:
diff --git a/chrome/browser/sync/engine/build_and_process_conflict_sets_command.cc b/chrome/browser/sync/engine/build_and_process_conflict_sets_command.cc
index 065f021..b4fc41e 100644
--- a/chrome/browser/sync/engine/build_and_process_conflict_sets_command.cc
+++ b/chrome/browser/sync/engine/build_and_process_conflict_sets_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -35,10 +35,11 @@ std::set<ModelSafeGroup> BuildAndProcessConflictSetsCommand::GetGroupsToChange(
   return session.GetEnabledGroupsWithConflicts();
 }
 
-void BuildAndProcessConflictSetsCommand::ModelChangingExecuteImpl(
+SyncerError BuildAndProcessConflictSetsCommand::ModelChangingExecuteImpl(
     SyncSession* session) {
   session->mutable_status_controller()->update_conflict_sets_built(
       BuildAndProcessConflictSets(session));
+  return SYNCER_OK;
 }
 
 bool BuildAndProcessConflictSetsCommand::BuildAndProcessConflictSets(
diff --git a/chrome/browser/sync/engine/build_and_process_conflict_sets_command.h b/chrome/browser/sync/engine/build_and_process_conflict_sets_command.h
index 8ef7b8d..1ae090d 100644
--- a/chrome/browser/sync/engine/build_and_process_conflict_sets_command.h
+++ b/chrome/browser/sync/engine/build_and_process_conflict_sets_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -39,7 +39,7 @@ class BuildAndProcessConflictSetsCommand : public ModelChangingSyncerCommand {
   // ModelChangingSyncerCommand implementation.
   virtual std::set<ModelSafeGroup> GetGroupsToChange(
       const sessions::SyncSession& session) const OVERRIDE;
-  virtual void ModelChangingExecuteImpl(
+  virtual SyncerError ModelChangingExecuteImpl(
       sessions::SyncSession* session) OVERRIDE;
 
  private:
diff --git a/chrome/browser/sync/engine/build_commit_command.cc b/chrome/browser/sync/engine/build_commit_command.cc
index 35ff047..4655827 100644
--- a/chrome/browser/sync/engine/build_commit_command.cc
+++ b/chrome/browser/sync/engine/build_commit_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -85,7 +85,7 @@ void SetEntrySpecifics(MutableEntry* meta_entry, SyncEntity* sync_entry) {
 }
 }  // namespace
 
-void BuildCommitCommand::ExecuteImpl(SyncSession* session) {
+SyncerError BuildCommitCommand::ExecuteImpl(SyncSession* session) {
   ClientToServerMessage message;
   message.set_share(session->context()->account_name());
   message.set_message_contents(ClientToServerMessage::COMMIT);
@@ -210,6 +210,8 @@ void BuildCommitCommand::ExecuteImpl(SyncSession* session) {
   }
   session->mutable_status_controller()->
       mutable_commit_message()->CopyFrom(message);
+
+  return SYNCER_OK;
 }
 
 int64 BuildCommitCommand::FindAnchorPosition(syncable::IdField direction,
diff --git a/chrome/browser/sync/engine/build_commit_command.h b/chrome/browser/sync/engine/build_commit_command.h
index ca7d412..fca2535 100644
--- a/chrome/browser/sync/engine/build_commit_command.h
+++ b/chrome/browser/sync/engine/build_commit_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -20,7 +20,7 @@ class BuildCommitCommand : public SyncerCommand {
   virtual ~BuildCommitCommand();
 
   // SyncerCommand implementation.
-  virtual void ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
+  virtual SyncerError ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
 
  private:
   FRIEND_TEST_ALL_PREFIXES(BuildCommitCommandTest, InterpolatePosition);
diff --git a/chrome/browser/sync/engine/cleanup_disabled_types_command.cc b/chrome/browser/sync/engine/cleanup_disabled_types_command.cc
index 49a0fda..7b73cf9 100644
--- a/chrome/browser/sync/engine/cleanup_disabled_types_command.cc
+++ b/chrome/browser/sync/engine/cleanup_disabled_types_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -17,10 +17,10 @@ namespace browser_sync {
 CleanupDisabledTypesCommand::CleanupDisabledTypesCommand() {}
 CleanupDisabledTypesCommand::~CleanupDisabledTypesCommand() {}
 
-void CleanupDisabledTypesCommand::ExecuteImpl(sessions::SyncSession* session) {
+SyncerError CleanupDisabledTypesCommand::ExecuteImpl(
+    sessions::SyncSession* session) {
   using syncable::ModelTypeSet;
   using syncable::ModelTypeSetToString;
-
   // Because a full directory purge is slow, we avoid purging
   // undesired types unless we have reason to believe they were
   // previously enabled.  Because purging could theoretically fail on
@@ -61,16 +61,17 @@ void CleanupDisabledTypesCommand::ExecuteImpl(sessions::SyncSession* session) {
            << ", to_cleanup = " << ModelTypeSetToString(to_cleanup);
 
   if (to_cleanup.Empty())
-    return;
+    return SYNCER_OK;
 
   syncable::ScopedDirLookup dir(session->context()->directory_manager(),
                                 session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   }
 
   dir->PurgeEntriesWithTypeIn(to_cleanup);
+  return SYNCER_OK;
 }
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/engine/cleanup_disabled_types_command.h b/chrome/browser/sync/engine/cleanup_disabled_types_command.h
index f5d2f40..70dece2 100644
--- a/chrome/browser/sync/engine/cleanup_disabled_types_command.h
+++ b/chrome/browser/sync/engine/cleanup_disabled_types_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -34,7 +34,7 @@ class CleanupDisabledTypesCommand : public SyncerCommand {
   virtual ~CleanupDisabledTypesCommand();
 
   // SyncerCommand implementation.
-  virtual void ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
+  virtual SyncerError ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CleanupDisabledTypesCommand);
diff --git a/chrome/browser/sync/engine/clear_data_command.cc b/chrome/browser/sync/engine/clear_data_command.cc
index 932c624..248fc83 100644
--- a/chrome/browser/sync/engine/clear_data_command.cc
+++ b/chrome/browser/sync/engine/clear_data_command.cc
@@ -26,7 +26,7 @@ using syncable::MODEL_TYPE_COUNT;
 ClearDataCommand::ClearDataCommand() {}
 ClearDataCommand::~ClearDataCommand() {}
 
-void ClearDataCommand::ExecuteImpl(SyncSession* session) {
+SyncerError ClearDataCommand::ExecuteImpl(SyncSession* session) {
   ClientToServerMessage client_to_server_message;
   ClientToServerResponse client_to_server_response;
 
@@ -40,7 +40,7 @@ void ClearDataCommand::ExecuteImpl(SyncSession* session) {
                       session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   }
 
   SyncerProtoUtil::AddRequestBirthday(dir, &client_to_server_message);
@@ -55,6 +55,11 @@ void ClearDataCommand::ExecuteImpl(SyncSession* session) {
   DVLOG(1) << SyncerProtoUtil::ClientToServerResponseDebugString(
       client_to_server_response);
 
+  // TODO(lipalani): This code is wrong.  The response error codes it checks
+  // have been obsoleted.  The only reason it hasn't caused problems is that
+  // this code is unreachable.  We should do something to clean up this mess.
+  // See also: crbug.com/71616.
+  //
   // Clear pending indicates that the server has received our clear message
   if (!ok || !client_to_server_response.has_error_code() ||
       client_to_server_response.error_code() != sync_pb::SyncEnums::SUCCESS) {
@@ -66,7 +71,7 @@ void ClearDataCommand::ExecuteImpl(SyncSession* session) {
 
     LOG(ERROR) << "Error posting ClearData.";
 
-    return;
+    return SYNCER_OK;
   }
 
   SyncEngineEvent event(SyncEngineEvent::CLEAR_SERVER_DATA_SUCCEEDED);
@@ -75,6 +80,7 @@ void ClearDataCommand::ExecuteImpl(SyncSession* session) {
   session->delegate()->OnShouldStopSyncingPermanently();
 
   DVLOG(1) << "ClearData succeeded.";
+  return SYNCER_OK;
 }
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/engine/clear_data_command.h b/chrome/browser/sync/engine/clear_data_command.h
index 763deef..f01a78c 100644
--- a/chrome/browser/sync/engine/clear_data_command.h
+++ b/chrome/browser/sync/engine/clear_data_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -20,7 +20,7 @@ class ClearDataCommand : public SyncerCommand {
   virtual ~ClearDataCommand();
 
   // SyncerCommand implementation.
-  virtual void ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
+  virtual SyncerError ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ClearDataCommand);
diff --git a/chrome/browser/sync/engine/download_updates_command.cc b/chrome/browser/sync/engine/download_updates_command.cc
index 86414a6e..8cee1b5 100644
--- a/chrome/browser/sync/engine/download_updates_command.cc
+++ b/chrome/browser/sync/engine/download_updates_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -30,7 +30,7 @@ using syncable::ModelTypeSetToString;
 DownloadUpdatesCommand::DownloadUpdatesCommand() {}
 DownloadUpdatesCommand::~DownloadUpdatesCommand() {}
 
-void DownloadUpdatesCommand::ExecuteImpl(SyncSession* session) {
+SyncerError DownloadUpdatesCommand::ExecuteImpl(SyncSession* session) {
   ClientToServerMessage client_to_server_message;
   ClientToServerResponse update_response;
 
@@ -48,7 +48,7 @@ void DownloadUpdatesCommand::ExecuteImpl(SyncSession* session) {
                       session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   }
 
   // Request updates for all enabled types.
@@ -105,7 +105,7 @@ void DownloadUpdatesCommand::ExecuteImpl(SyncSession* session) {
     status->increment_num_consecutive_errors();
     status->mutable_updates_response()->Clear();
     LOG(ERROR) << "PostClientToServerMessage() failed during GetUpdates";
-    return;
+    return SYNCER_OK; // TODO(rlarocque): Return an error here.
   }
 
   status->mutable_updates_response()->CopyFrom(update_response);
@@ -115,6 +115,7 @@ void DownloadUpdatesCommand::ExecuteImpl(SyncSession* session) {
            << " updates and indicated "
            << update_response.get_updates().changes_remaining()
            << " updates left on server.";
+  return SYNCER_OK;
 }
 
 void DownloadUpdatesCommand::AppendClientDebugInfoIfNeeded(
diff --git a/chrome/browser/sync/engine/download_updates_command.h b/chrome/browser/sync/engine/download_updates_command.h
index 293c99a..3b12c71 100644
--- a/chrome/browser/sync/engine/download_updates_command.h
+++ b/chrome/browser/sync/engine/download_updates_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -44,7 +44,7 @@ class DownloadUpdatesCommand : public SyncerCommand {
   virtual ~DownloadUpdatesCommand();
 
   // SyncerCommand implementation.
-  virtual void ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
+  virtual SyncerError ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
 
  private:
   FRIEND_TEST_ALL_PREFIXES(DownloadUpdatesCommandTest, VerifyAppendDebugInfo);
diff --git a/chrome/browser/sync/engine/get_commit_ids_command.cc b/chrome/browser/sync/engine/get_commit_ids_command.cc
index 720c063..f4beb4b 100644
--- a/chrome/browser/sync/engine/get_commit_ids_command.cc
+++ b/chrome/browser/sync/engine/get_commit_ids_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -29,7 +29,7 @@ GetCommitIdsCommand::GetCommitIdsCommand(int commit_batch_size)
 
 GetCommitIdsCommand::~GetCommitIdsCommand() {}
 
-void GetCommitIdsCommand::ExecuteImpl(SyncSession* session) {
+SyncerError GetCommitIdsCommand::ExecuteImpl(SyncSession* session) {
   // Gather the full set of unsynced items and store it in the session. They
   // are not in the correct order for commit.
   syncable::Directory::UnsyncedMetaHandles all_unsynced_handles;
@@ -65,6 +65,7 @@ void GetCommitIdsCommand::ExecuteImpl(SyncSession* session) {
     DVLOG(1) << "Debug commit batch result:" << verified_commit_ids[i];
 
   status->set_commit_set(*ordered_commit_set_.get());
+  return SYNCER_OK;
 }
 
 namespace {
diff --git a/chrome/browser/sync/engine/get_commit_ids_command.h b/chrome/browser/sync/engine/get_commit_ids_command.h
index b728671..cff27b5 100644
--- a/chrome/browser/sync/engine/get_commit_ids_command.h
+++ b/chrome/browser/sync/engine/get_commit_ids_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -28,7 +28,7 @@ class GetCommitIdsCommand : public SyncerCommand {
   virtual ~GetCommitIdsCommand();
 
   // SyncerCommand implementation.
-  virtual void ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
+  virtual SyncerError ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
 
   // Builds a vector of IDs that should be committed.
   void BuildCommitIds(const vector<int64>& unsynced_handles,
diff --git a/chrome/browser/sync/engine/model_changing_syncer_command.cc b/chrome/browser/sync/engine/model_changing_syncer_command.cc
index 1c392cb..cd99da9 100644
--- a/chrome/browser/sync/engine/model_changing_syncer_command.cc
+++ b/chrome/browser/sync/engine/model_changing_syncer_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -9,15 +9,16 @@
 #include "base/bind_helpers.h"
 #include "chrome/browser/sync/sessions/status_controller.h"
 #include "chrome/browser/sync/sessions/sync_session.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
 
 namespace browser_sync {
 
-void ModelChangingSyncerCommand::ExecuteImpl(sessions::SyncSession* session) {
+SyncerError ModelChangingSyncerCommand::ExecuteImpl(
+    sessions::SyncSession* session) {
   work_session_ = session;
-  if (!ModelNeutralExecuteImpl(work_session_)) {
-    return;
-  }
+  SyncerError result = ModelNeutralExecuteImpl(work_session_);
+
+  if (result != SYNCER_OK)
+    return result;
 
   const std::set<ModelSafeGroup>& groups_to_change =
       GetGroupsToChange(*work_session_);
@@ -40,15 +41,19 @@ void ModelChangingSyncerCommand::ExecuteImpl(sessions::SyncSession* session) {
         // unretained.
         base::Unretained(this));
 
-    // TODO(lipalani): Check the return value for an unrecoverable error.
-    ignore_result(worker->DoWorkAndWaitUntilDone(c));
-
+    SyncerError this_worker_result = worker->DoWorkAndWaitUntilDone(c);
+    // TODO(rlarocque): Figure out a better way to deal with errors from
+    // multiple models at once.  See also: crbug.com/109422.
+    if (this_worker_result != SYNCER_OK)
+      result = this_worker_result;
   }
+
+  return result;
 }
 
-bool ModelChangingSyncerCommand::ModelNeutralExecuteImpl(
+SyncerError ModelChangingSyncerCommand::ModelNeutralExecuteImpl(
     sessions::SyncSession* session) {
-  return true;
+  return SYNCER_OK;
 }
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/engine/model_changing_syncer_command.h b/chrome/browser/sync/engine/model_changing_syncer_command.h
index e6f6ca1..c11b6a3 100644
--- a/chrome/browser/sync/engine/model_changing_syncer_command.h
+++ b/chrome/browser/sync/engine/model_changing_syncer_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -9,7 +9,6 @@
 #include "base/compiler_specific.h"
 #include "chrome/browser/sync/engine/model_safe_worker.h"
 #include "chrome/browser/sync/engine/syncer_command.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
 
 namespace browser_sync {
 namespace sessions {
@@ -32,14 +31,12 @@ class ModelChangingSyncerCommand : public SyncerCommand {
   virtual ~ModelChangingSyncerCommand() { }
 
   // SyncerCommand implementation. Sets work_session to session.
-  virtual void ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
+  virtual browser_sync::SyncerError ExecuteImpl(
+      sessions::SyncSession* session) OVERRIDE;
 
-  // wrapper so implementations don't worry about storing work_session
-  UnrecoverableErrorInfo StartChangingModel() {
-    // TODO(lipalani): |ModelChangingExecuteImpl| should return an
-    // UnrecoverableErrorInfo struct.
-    ModelChangingExecuteImpl(work_session_);
-    return UnrecoverableErrorInfo();
+  // Wrapper so implementations don't worry about storing work_session.
+  SyncerError StartChangingModel() {
+    return ModelChangingExecuteImpl(work_session_);
   }
 
   std::set<ModelSafeGroup> GetGroupsToChangeForTest(
@@ -64,13 +61,14 @@ class ModelChangingSyncerCommand : public SyncerCommand {
   // *without* a ModelSafeGroup restriction in place on the SyncSession.
   // Returns true on success, false on failure.
   // TODO(tim): Remove this (bug 36594).
-  virtual bool ModelNeutralExecuteImpl(sessions::SyncSession* session);
+  virtual SyncerError ModelNeutralExecuteImpl(sessions::SyncSession* session);
 
   // Abstract method to be implemented by subclasses to handle logic that
   // operates on the model.  This is invoked with a SyncSession ModelSafeGroup
   // restriction in place so that bits of state belonging to data types
   // running on an unsafe thread are siloed away.
-  virtual void ModelChangingExecuteImpl(sessions::SyncSession* session) = 0;
+  virtual SyncerError ModelChangingExecuteImpl(
+      sessions::SyncSession* session) = 0;
 
  private:
   // ExecuteImpl is expected to be run by SyncerCommand to set work_session.
diff --git a/chrome/browser/sync/engine/model_changing_syncer_command_unittest.cc b/chrome/browser/sync/engine/model_changing_syncer_command_unittest.cc
index 93736de..1e9d1d13 100644
--- a/chrome/browser/sync/engine/model_changing_syncer_command_unittest.cc
+++ b/chrome/browser/sync/engine/model_changing_syncer_command_unittest.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -31,9 +31,10 @@ class FakeModelChangingSyncerCommand : public ModelChangingSyncerCommand {
     return session.GetEnabledGroups();
   }
 
-  virtual void ModelChangingExecuteImpl(
+  virtual SyncerError ModelChangingExecuteImpl(
       sessions::SyncSession* session) OVERRIDE {
     changed_groups_.insert(session->status_controller().group_restriction());
+    return SYNCER_OK;
   }
 
  private:
diff --git a/chrome/browser/sync/engine/model_safe_worker.cc b/chrome/browser/sync/engine/model_safe_worker.cc
index eb2b903..3c5bcbf 100644
--- a/chrome/browser/sync/engine/model_safe_worker.cc
+++ b/chrome/browser/sync/engine/model_safe_worker.cc
@@ -1,9 +1,8 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
 #include "chrome/browser/sync/engine/model_safe_worker.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
 
 #include "base/json/json_writer.h"
 #include "base/memory/scoped_ptr.h"
diff --git a/chrome/browser/sync/engine/model_safe_worker.h b/chrome/browser/sync/engine/model_safe_worker.h
index a103d09..8ed3448 100644
--- a/chrome/browser/sync/engine/model_safe_worker.h
+++ b/chrome/browser/sync/engine/model_safe_worker.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -12,8 +12,8 @@
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
+#include "chrome/browser/sync/internal_api/includes/syncer_error.h"
 #include "chrome/browser/sync/syncable/model_type.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
 
 namespace base {
 class DictionaryValue;
@@ -21,7 +21,7 @@ class DictionaryValue;
 
 namespace browser_sync {
 
-typedef base::Callback<UnrecoverableErrorInfo(void)> WorkCallback;
+typedef base::Callback<enum SyncerError(void)> WorkCallback;
 
 enum ModelSafeGroup {
   GROUP_PASSIVE = 0,   // Models that are just "passively" being synced; e.g.
@@ -52,8 +52,7 @@ class ModelSafeWorker : public base::RefCountedThreadSafe<ModelSafeWorker> {
   // Any time the Syncer performs model modifications (e.g employing a
   // WriteTransaction), it should be done by this method to ensure it is done
   // from a model-safe thread.
-  virtual UnrecoverableErrorInfo DoWorkAndWaitUntilDone(
-      const WorkCallback& work) = 0;
+  virtual SyncerError DoWorkAndWaitUntilDone(const WorkCallback& work) = 0;
 
   virtual ModelSafeGroup GetModelSafeGroup() = 0;
 
diff --git a/chrome/browser/sync/engine/passive_model_worker.cc b/chrome/browser/sync/engine/passive_model_worker.cc
index d98b451..64be1b1 100644
--- a/chrome/browser/sync/engine/passive_model_worker.cc
+++ b/chrome/browser/sync/engine/passive_model_worker.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -14,7 +14,7 @@ PassiveModelWorker::PassiveModelWorker(const MessageLoop* sync_loop)
 PassiveModelWorker::~PassiveModelWorker() {
 }
 
-UnrecoverableErrorInfo PassiveModelWorker::DoWorkAndWaitUntilDone(
+SyncerError PassiveModelWorker::DoWorkAndWaitUntilDone(
     const WorkCallback& work) {
   DCHECK_EQ(MessageLoop::current(), sync_loop_);
   // Simply do the work on the current thread.
diff --git a/chrome/browser/sync/engine/passive_model_worker.h b/chrome/browser/sync/engine/passive_model_worker.h
index 7574380..5a35b0a2 100644
--- a/chrome/browser/sync/engine/passive_model_worker.h
+++ b/chrome/browser/sync/engine/passive_model_worker.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -9,6 +9,7 @@
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "chrome/browser/sync/engine/model_safe_worker.h"
+#include "chrome/browser/sync/internal_api/includes/syncer_error.h"
 
 class MessageLoop;
 
@@ -22,7 +23,7 @@ class PassiveModelWorker : public ModelSafeWorker {
   explicit PassiveModelWorker(const MessageLoop* sync_loop);
 
   // ModelSafeWorker implementation. Called on the sync thread.
-  virtual UnrecoverableErrorInfo DoWorkAndWaitUntilDone(
+  virtual SyncerError DoWorkAndWaitUntilDone(
       const WorkCallback& work) OVERRIDE;
   virtual ModelSafeGroup GetModelSafeGroup() OVERRIDE;
 
diff --git a/chrome/browser/sync/engine/post_commit_message_command.cc b/chrome/browser/sync/engine/post_commit_message_command.cc
index c70a193..4379a80 100644
--- a/chrome/browser/sync/engine/post_commit_message_command.cc
+++ b/chrome/browser/sync/engine/post_commit_message_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -19,14 +19,15 @@ namespace browser_sync {
 PostCommitMessageCommand::PostCommitMessageCommand() {}
 PostCommitMessageCommand::~PostCommitMessageCommand() {}
 
-void PostCommitMessageCommand::ExecuteImpl(sessions::SyncSession* session) {
+SyncerError PostCommitMessageCommand::ExecuteImpl(
+    sessions::SyncSession* session) {
   if (session->status_controller().commit_ids().empty())
-    return;  // Nothing to commit.
+    return SYNCER_OK;  // Nothing to commit.
   ClientToServerResponse response;
   syncable::ScopedDirLookup dir(session->context()->directory_manager(),
                                 session->context()->account_name());
   if (!dir.good())
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   sessions::StatusController* status = session->mutable_status_controller();
   if (!SyncerProtoUtil::PostClientToServerMessage(status->commit_message(),
           &response, session)) {
@@ -41,11 +42,13 @@ void PostCommitMessageCommand::ExecuteImpl(sessions::SyncSession* session) {
       syncable::MutableEntry entry(&trans, syncable::GET_BY_ID, commit_ids[i]);
       entry.Put(syncable::SYNCING, false);
     }
-    return;
+    return SYNCER_OK; // TODO(rlarocque): Return an error here.
   } else {
     status->set_items_committed();
   }
+
   status->mutable_commit_response()->CopyFrom(response);
+  return SYNCER_OK;
 }
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/engine/post_commit_message_command.h b/chrome/browser/sync/engine/post_commit_message_command.h
index 6470bb6..5f2252c 100644
--- a/chrome/browser/sync/engine/post_commit_message_command.h
+++ b/chrome/browser/sync/engine/post_commit_message_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -17,7 +17,7 @@ class PostCommitMessageCommand : public SyncerCommand {
   virtual ~PostCommitMessageCommand();
 
   // SyncerCommand implementation.
-  virtual void ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
+  virtual SyncerError ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PostCommitMessageCommand);
diff --git a/chrome/browser/sync/engine/process_commit_response_command.cc b/chrome/browser/sync/engine/process_commit_response_command.cc
index a4c3291..43ec2ca 100644
--- a/chrome/browser/sync/engine/process_commit_response_command.cc
+++ b/chrome/browser/sync/engine/process_commit_response_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -81,13 +81,13 @@ std::set<ModelSafeGroup> ProcessCommitResponseCommand::GetGroupsToChange(
   return groups_with_commits;
 }
 
-bool ProcessCommitResponseCommand::ModelNeutralExecuteImpl(
+SyncerError ProcessCommitResponseCommand::ModelNeutralExecuteImpl(
     sessions::SyncSession* session) {
   ScopedDirLookup dir(session->context()->directory_manager(),
                       session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
-    return false;
+    return DIRECTORY_LOOKUP_FAILED;
   }
 
   const StatusController& status = session->status_controller();
@@ -98,7 +98,7 @@ bool ProcessCommitResponseCommand::ModelNeutralExecuteImpl(
     // TODO(sync): What if we didn't try to commit anything?
     LOG(WARNING) << "Commit response has no commit body!";
     IncrementErrorCounters(session->mutable_status_controller());
-    return false;
+    return SERVER_RESPONSE_VALIDATION_FAILED;
   }
 
   const CommitResponse& cr = response.commit();
@@ -113,14 +113,14 @@ bool ProcessCommitResponseCommand::ModelNeutralExecuteImpl(
         LOG(ERROR) << "  " << cr.entryresponse(i).error_message();
     }
     IncrementErrorCounters(session->mutable_status_controller());
-    return false;
+    return SERVER_RESPONSE_VALIDATION_FAILED;
   }
-  return true;
+  return SYNCER_OK;
 }
 
-void ProcessCommitResponseCommand::ModelChangingExecuteImpl(
+SyncerError ProcessCommitResponseCommand::ModelChangingExecuteImpl(
     SyncSession* session) {
-  ProcessCommitResponse(session);
+  SyncerError result = ProcessCommitResponse(session);
   ExtensionsActivityMonitor* monitor = session->context()->extensions_monitor();
   if (session->status_controller().HasBookmarkCommitActivity() &&
       session->status_controller().syncer_status()
@@ -128,17 +128,16 @@ void ProcessCommitResponseCommand::ModelChangingExecuteImpl(
     monitor->PutRecords(session->extensions_activity());
     session->mutable_extensions_activity()->clear();
   }
+  return result;
 }
 
-void ProcessCommitResponseCommand::ProcessCommitResponse(
+SyncerError ProcessCommitResponseCommand::ProcessCommitResponse(
     SyncSession* session) {
-  // TODO(sync): This function returns if it sees problems. We probably want
-  // to flag the need for an update or similar.
   ScopedDirLookup dir(session->context()->directory_manager(),
                       session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   }
 
   StatusController* status = session->mutable_status_controller();
@@ -189,10 +188,6 @@ void ProcessCommitResponseCommand::ProcessCommitResponse(
           // We handle over quota like a retry, which is same as transient.
         case CommitResponse::RETRY:
         case CommitResponse::TRANSIENT_ERROR:
-          // TODO(tim): Now that we have SyncSession::Delegate, we
-          // should plumb this directly for exponential backoff purposes rather
-          // than trying to infer from HasMoreToSync(). See
-          // SyncerThread::CalculatePollingWaitTime.
           ++transient_error_commits;
           break;
         default:
@@ -218,7 +213,20 @@ void ProcessCommitResponseCommand::ProcessCommitResponse(
   }
   SyncerUtil::MarkDeletedChildrenSynced(dir, &deleted_folders);
 
-  return;
+  if (commit_count == (successes + conflicting_commits)) {
+    // We consider conflicting commits as a success because things will work out
+    // on their own when we receive them.  Flags will be set so that
+    // HasMoreToSync() will cause SyncScheduler to enter another sync cycle to
+    // handle this condition.
+    return SYNCER_OK;
+  } else if (error_commits > 0) {
+    return SERVER_RETURN_UNKNOWN_ERROR;
+  } else if (transient_error_commits > 0) {
+    return SERVER_RETURN_TRANSIENT_ERROR;
+  } else {
+    LOG(FATAL) << "Inconsistent counts when processing commit response";
+    return SYNCER_OK;
+  }
 }
 
 void LogServerError(const CommitResponse_EntryResponse& res) {
diff --git a/chrome/browser/sync/engine/process_commit_response_command.h b/chrome/browser/sync/engine/process_commit_response_command.h
index bac2a31..e6762a2 100644
--- a/chrome/browser/sync/engine/process_commit_response_command.h
+++ b/chrome/browser/sync/engine/process_commit_response_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -32,9 +32,9 @@ class ProcessCommitResponseCommand : public ModelChangingSyncerCommand {
   // ModelChangingSyncerCommand implementation.
   virtual std::set<ModelSafeGroup> GetGroupsToChange(
       const sessions::SyncSession& session) const OVERRIDE;
-  virtual bool ModelNeutralExecuteImpl(
+  virtual SyncerError ModelNeutralExecuteImpl(
       sessions::SyncSession* session) OVERRIDE;
-  virtual void ModelChangingExecuteImpl(
+  virtual SyncerError ModelChangingExecuteImpl(
       sessions::SyncSession* session) OVERRIDE;
 
  private:
@@ -47,7 +47,7 @@ class ProcessCommitResponseCommand : public ModelChangingSyncerCommand {
       std::set<syncable::Id>* deleted_folders);
 
   // Actually does the work of execute.
-  void ProcessCommitResponse(sessions::SyncSession* session);
+  SyncerError ProcessCommitResponse(sessions::SyncSession* session);
 
   void ProcessSuccessfulCommitResponse(
       const sync_pb::SyncEntity& committed_entry,
diff --git a/chrome/browser/sync/engine/process_updates_command.cc b/chrome/browser/sync/engine/process_updates_command.cc
index 7ab56d5..d9d397e 100644
--- a/chrome/browser/sync/engine/process_updates_command.cc
+++ b/chrome/browser/sync/engine/process_updates_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -33,18 +33,19 @@ std::set<ModelSafeGroup> ProcessUpdatesCommand::GetGroupsToChange(
   return session.GetEnabledGroupsWithVerifiedUpdates();
 }
 
-void ProcessUpdatesCommand::ModelChangingExecuteImpl(SyncSession* session) {
+SyncerError ProcessUpdatesCommand::ModelChangingExecuteImpl(
+    SyncSession* session) {
   syncable::ScopedDirLookup dir(session->context()->directory_manager(),
                                 session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   }
 
   const sessions::UpdateProgress* progress =
       session->status_controller().update_progress();
   if (!progress)
-    return;  // Nothing to do.
+    return SYNCER_OK;  // Nothing to do.
 
   syncable::WriteTransaction trans(FROM_HERE, syncable::SYNCER, dir);
   vector<sessions::VerifiedUpdate>::const_iterator it;
@@ -70,6 +71,7 @@ void ProcessUpdatesCommand::ModelChangingExecuteImpl(SyncSession* session) {
   StatusController* status = session->mutable_status_controller();
   status->set_num_consecutive_errors(0);
   status->mutable_update_progress()->ClearVerifiedUpdates();
+  return SYNCER_OK;
 }
 
 namespace {
diff --git a/chrome/browser/sync/engine/process_updates_command.h b/chrome/browser/sync/engine/process_updates_command.h
index d5dd2be..11fb1e2 100644
--- a/chrome/browser/sync/engine/process_updates_command.h
+++ b/chrome/browser/sync/engine/process_updates_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -40,7 +40,7 @@ class ProcessUpdatesCommand : public ModelChangingSyncerCommand {
   // ModelChangingSyncerCommand implementation.
   virtual std::set<ModelSafeGroup> GetGroupsToChange(
       const sessions::SyncSession& session) const OVERRIDE;
-  virtual void ModelChangingExecuteImpl(
+  virtual SyncerError ModelChangingExecuteImpl(
       sessions::SyncSession* session) OVERRIDE;
 
  private:
diff --git a/chrome/browser/sync/engine/resolve_conflicts_command.cc b/chrome/browser/sync/engine/resolve_conflicts_command.cc
index e76b1c7..b175d74 100644
--- a/chrome/browser/sync/engine/resolve_conflicts_command.cc
+++ b/chrome/browser/sync/engine/resolve_conflicts_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -19,26 +19,26 @@ std::set<ModelSafeGroup> ResolveConflictsCommand::GetGroupsToChange(
   return session.GetEnabledGroupsWithConflicts();
 }
 
-void ResolveConflictsCommand::ModelChangingExecuteImpl(
+SyncerError ResolveConflictsCommand::ModelChangingExecuteImpl(
     sessions::SyncSession* session) {
   ConflictResolver* resolver = session->context()->resolver();
   DCHECK(resolver);
-  if (!resolver)
-    return;
 
   syncable::ScopedDirLookup dir(session->context()->directory_manager(),
                                 session->context()->account_name());
   if (!dir.good())
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   sessions::StatusController* status = session->mutable_status_controller();
   const sessions::ConflictProgress* progress = status->conflict_progress();
   if (!progress)
-    return;  // Nothing to do.
+    return SYNCER_OK;  // Nothing to do.
   syncable::WriteTransaction trans(FROM_HERE, syncable::SYNCER, dir);
   const Cryptographer* cryptographer =
       session->context()->directory_manager()->GetCryptographer(&trans);
   status->update_conflicts_resolved(
       resolver->ResolveConflicts(&trans, cryptographer, *progress, status));
+
+  return SYNCER_OK;
 }
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/engine/resolve_conflicts_command.h b/chrome/browser/sync/engine/resolve_conflicts_command.h
index 2407593..2121a31 100644
--- a/chrome/browser/sync/engine/resolve_conflicts_command.h
+++ b/chrome/browser/sync/engine/resolve_conflicts_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -21,7 +21,7 @@ class ResolveConflictsCommand : public ModelChangingSyncerCommand {
   // ModelChangingSyncerCommand implementation.
   virtual std::set<ModelSafeGroup> GetGroupsToChange(
       const sessions::SyncSession& session) const OVERRIDE;
-  virtual void ModelChangingExecuteImpl(
+  virtual SyncerError ModelChangingExecuteImpl(
       sessions::SyncSession* session) OVERRIDE;
 
  private:
diff --git a/chrome/browser/sync/engine/store_timestamps_command.cc b/chrome/browser/sync/engine/store_timestamps_command.cc
index 140191b..64bc5be 100644
--- a/chrome/browser/sync/engine/store_timestamps_command.cc
+++ b/chrome/browser/sync/engine/store_timestamps_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -15,13 +15,14 @@ namespace browser_sync {
 StoreTimestampsCommand::StoreTimestampsCommand() {}
 StoreTimestampsCommand::~StoreTimestampsCommand() {}
 
-void StoreTimestampsCommand::ExecuteImpl(sessions::SyncSession* session) {
+SyncerError StoreTimestampsCommand::ExecuteImpl(
+    sessions::SyncSession* session) {
   syncable::ScopedDirLookup dir(session->context()->directory_manager(),
                                 session->context()->account_name());
 
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   }
 
   const GetUpdatesResponse& updates =
@@ -58,6 +59,8 @@ void StoreTimestampsCommand::ExecuteImpl(sessions::SyncSession* session) {
     DVLOG(1) << "Changes remaining: " << changes_left;
     status->set_num_server_changes_remaining(changes_left);
   }
+
+  return SYNCER_OK;
 }
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/engine/store_timestamps_command.h b/chrome/browser/sync/engine/store_timestamps_command.h
index c05c2e6..cbc7c83 100644
--- a/chrome/browser/sync/engine/store_timestamps_command.h
+++ b/chrome/browser/sync/engine/store_timestamps_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -30,7 +30,7 @@ class StoreTimestampsCommand : public SyncerCommand {
   virtual ~StoreTimestampsCommand();
 
   // SyncerCommand implementation.
-  virtual void ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
+  virtual SyncerError ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(StoreTimestampsCommand);
diff --git a/chrome/browser/sync/engine/syncer_command.cc b/chrome/browser/sync/engine/syncer_command.cc
index 44e5477..ef2a558 100644
--- a/chrome/browser/sync/engine/syncer_command.cc
+++ b/chrome/browser/sync/engine/syncer_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -14,9 +14,10 @@ using sessions::SyncSession;
 SyncerCommand::SyncerCommand() {}
 SyncerCommand::~SyncerCommand() {}
 
-void SyncerCommand::Execute(SyncSession* session) {
-  ExecuteImpl(session);
+SyncerError SyncerCommand::Execute(SyncSession* session) {
+  SyncerError result = ExecuteImpl(session);
   SendNotifications(session);
+  return result;
 }
 
 void SyncerCommand::SendNotifications(SyncSession* session) {
diff --git a/chrome/browser/sync/engine/syncer_command.h b/chrome/browser/sync/engine/syncer_command.h
index 2aad653..024bbae 100644
--- a/chrome/browser/sync/engine/syncer_command.h
+++ b/chrome/browser/sync/engine/syncer_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -8,6 +8,8 @@
 
 #include "base/basictypes.h"
 
+#include "chrome/browser/sync/internal_api/includes/syncer_error.h"
+
 namespace browser_sync {
 
 namespace sessions {
@@ -32,10 +34,10 @@ class SyncerCommand {
   virtual ~SyncerCommand();
 
   // Execute dispatches to a derived class's ExecuteImpl.
-  void Execute(sessions::SyncSession* session);
+  SyncerError Execute(sessions::SyncSession* session);
 
   // ExecuteImpl is where derived classes actually do work.
-  virtual void ExecuteImpl(sessions::SyncSession* session) = 0;
+  virtual SyncerError ExecuteImpl(sessions::SyncSession* session) = 0;
  private:
   void SendNotifications(sessions::SyncSession* session);
   DISALLOW_COPY_AND_ASSIGN(SyncerCommand);
diff --git a/chrome/browser/sync/engine/verify_updates_command.cc b/chrome/browser/sync/engine/verify_updates_command.cc
index 96dd4e7..4b5a8ff 100644
--- a/chrome/browser/sync/engine/verify_updates_command.cc
+++ b/chrome/browser/sync/engine/verify_updates_command.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -42,14 +42,14 @@ std::set<ModelSafeGroup> VerifyUpdatesCommand::GetGroupsToChange(
   return groups_with_updates;
 }
 
-void VerifyUpdatesCommand::ModelChangingExecuteImpl(
+SyncerError VerifyUpdatesCommand::ModelChangingExecuteImpl(
     sessions::SyncSession* session) {
   DVLOG(1) << "Beginning Update Verification";
   ScopedDirLookup dir(session->context()->directory_manager(),
                       session->context()->account_name());
   if (!dir.good()) {
     LOG(ERROR) << "Scoped dir lookup failed!";
-    return;
+    return DIRECTORY_LOOKUP_FAILED;
   }
   WriteTransaction trans(FROM_HERE, SYNCER, dir);
   sessions::StatusController* status = session->mutable_status_controller();
@@ -72,6 +72,8 @@ void VerifyUpdatesCommand::ModelChangingExecuteImpl(
     if (update.deleted())
       status->increment_num_tombstone_updates_downloaded_by(1);
   }
+
+  return SYNCER_OK;
 }
 
 namespace {
diff --git a/chrome/browser/sync/engine/verify_updates_command.h b/chrome/browser/sync/engine/verify_updates_command.h
index 26b0b37..5c6ff05 100644
--- a/chrome/browser/sync/engine/verify_updates_command.h
+++ b/chrome/browser/sync/engine/verify_updates_command.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -30,7 +30,7 @@ class VerifyUpdatesCommand : public ModelChangingSyncerCommand {
   // ModelChangingSyncerCommand implementation.
   virtual std::set<ModelSafeGroup> GetGroupsToChange(
       const sessions::SyncSession& session) const OVERRIDE;
-  virtual void ModelChangingExecuteImpl(
+  virtual SyncerError ModelChangingExecuteImpl(
       sessions::SyncSession* session) OVERRIDE;
 
  private:
diff --git a/chrome/browser/sync/glue/browser_thread_model_worker.cc b/chrome/browser/sync/glue/browser_thread_model_worker.cc
index 91baabe..8fe5ebf 100644
--- a/chrome/browser/sync/glue/browser_thread_model_worker.cc
+++ b/chrome/browser/sync/glue/browser_thread_model_worker.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -19,9 +19,9 @@ BrowserThreadModelWorker::BrowserThreadModelWorker(
 
 BrowserThreadModelWorker::~BrowserThreadModelWorker() {}
 
-UnrecoverableErrorInfo BrowserThreadModelWorker::DoWorkAndWaitUntilDone(
+SyncerError BrowserThreadModelWorker::DoWorkAndWaitUntilDone(
     const WorkCallback& work) {
-  UnrecoverableErrorInfo error_info;
+  SyncerError error = UNSET;
   if (BrowserThread::CurrentlyOn(thread_)) {
     DLOG(WARNING) << "Already on thread " << thread_;
     return work.Run();
@@ -31,20 +31,20 @@ UnrecoverableErrorInfo BrowserThreadModelWorker::DoWorkAndWaitUntilDone(
       thread_,
       FROM_HERE,
       base::Bind(&BrowserThreadModelWorker::CallDoWorkAndSignalTask, this,
-                 work, &done, &error_info))) {
+                 work, &done, &error))) {
     NOTREACHED() << "Failed to post task to thread " << thread_;
-    return error_info;
+    return error;
   }
   done.Wait();
-  return error_info;
+  return error;
 }
 
 void BrowserThreadModelWorker::CallDoWorkAndSignalTask(
     const WorkCallback& work,
     WaitableEvent* done,
-    UnrecoverableErrorInfo* error_info) {
+    SyncerError* error) {
   DCHECK(BrowserThread::CurrentlyOn(thread_));
-  *error_info = work.Run();
+  *error = work.Run();
   done->Signal();
 }
 
@@ -60,8 +60,8 @@ DatabaseModelWorker::~DatabaseModelWorker() {}
 void DatabaseModelWorker::CallDoWorkAndSignalTask(
     const WorkCallback& work,
     WaitableEvent* done,
-    UnrecoverableErrorInfo* error_info) {
-  BrowserThreadModelWorker::CallDoWorkAndSignalTask(work, done, error_info);
+    SyncerError* error) {
+  BrowserThreadModelWorker::CallDoWorkAndSignalTask(work, done, error);
 }
 
 FileModelWorker::FileModelWorker()
@@ -72,8 +72,8 @@ FileModelWorker::~FileModelWorker() {}
 void FileModelWorker::CallDoWorkAndSignalTask(
     const WorkCallback& work,
     WaitableEvent* done,
-    UnrecoverableErrorInfo* error_info) {
-  BrowserThreadModelWorker::CallDoWorkAndSignalTask(work, done, error_info);
+    SyncerError* error) {
+  BrowserThreadModelWorker::CallDoWorkAndSignalTask(work, done, error);
 }
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/glue/browser_thread_model_worker.h b/chrome/browser/sync/glue/browser_thread_model_worker.h
index 6447b7f..b053fa6 100644
--- a/chrome/browser/sync/glue/browser_thread_model_worker.h
+++ b/chrome/browser/sync/glue/browser_thread_model_worker.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -10,7 +10,7 @@
 #include "base/callback_forward.h"
 #include "base/compiler_specific.h"
 #include "chrome/browser/sync/engine/model_safe_worker.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
+#include "chrome/browser/sync/internal_api/includes/syncer_error.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace base {
@@ -29,7 +29,7 @@ class BrowserThreadModelWorker : public ModelSafeWorker {
   virtual ~BrowserThreadModelWorker();
 
   // ModelSafeWorker implementation. Called on the sync thread.
-  virtual UnrecoverableErrorInfo DoWorkAndWaitUntilDone(
+  virtual SyncerError DoWorkAndWaitUntilDone(
       const WorkCallback& work) OVERRIDE;
   virtual ModelSafeGroup GetModelSafeGroup() OVERRIDE;
 
@@ -40,7 +40,7 @@ class BrowserThreadModelWorker : public ModelSafeWorker {
   virtual void CallDoWorkAndSignalTask(
       const WorkCallback& work,
       base::WaitableEvent* done,
-      UnrecoverableErrorInfo* error_info) = 0;
+      SyncerError* error) = 0;
 
  private:
   content::BrowserThread::ID thread_;
@@ -61,7 +61,7 @@ class DatabaseModelWorker : public BrowserThreadModelWorker {
   virtual void CallDoWorkAndSignalTask(
       const WorkCallback& work,
       base::WaitableEvent* done,
-      UnrecoverableErrorInfo* error_info) OVERRIDE;
+      SyncerError* error) OVERRIDE;
 };
 
 class FileModelWorker : public BrowserThreadModelWorker {
@@ -73,7 +73,7 @@ class FileModelWorker : public BrowserThreadModelWorker {
   virtual void CallDoWorkAndSignalTask(
       const WorkCallback& work,
       base::WaitableEvent* done,
-      UnrecoverableErrorInfo* error_info) OVERRIDE;
+      SyncerError* error) OVERRIDE;
 };
 
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/glue/browser_thread_model_worker_unittest.cc b/chrome/browser/sync/glue/browser_thread_model_worker_unittest.cc
index 4c6881a..fda74e0 100644
--- a/chrome/browser/sync/glue/browser_thread_model_worker_unittest.cc
+++ b/chrome/browser/sync/glue/browser_thread_model_worker_unittest.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -11,7 +11,6 @@
 #include "base/threading/thread.h"
 #include "base/timer.h"
 #include "chrome/browser/sync/glue/browser_thread_model_worker.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
 #include "content/test/test_browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -54,13 +53,13 @@ class BrowserThreadModelWorkerTest : public testing::Test {
   }
 
   // This is the work that will be scheduled to be done on the DB thread.
-  UnrecoverableErrorInfo DoWork() {
+  SyncerError DoWork() {
     EXPECT_TRUE(BrowserThread::CurrentlyOn(BrowserThread::DB));
     timer_.Stop();  // Stop the failure timer so the test succeeds.
     BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE, MessageLoop::QuitClosure());
     did_do_work_ = true;
-    return UnrecoverableErrorInfo();
+    return SYNCER_OK;
   }
 
   // This will be called by the OneShotTimer and make the test fail unless
diff --git a/chrome/browser/sync/glue/history_model_worker.cc b/chrome/browser/sync/glue/history_model_worker.cc
index 88a8193..35d459d 100644
--- a/chrome/browser/sync/glue/history_model_worker.cc
+++ b/chrome/browser/sync/glue/history_model_worker.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -18,12 +18,12 @@ class WorkerTask : public HistoryDBTask {
   WorkerTask(
       const WorkCallback& work,
       WaitableEvent* done,
-      UnrecoverableErrorInfo* error_info)
-    : work_(work), done_(done), error_info_(error_info) {}
+      SyncerError* error)
+    : work_(work), done_(done), error_(error) {}
 
   virtual bool RunOnDBThread(history::HistoryBackend* backend,
                              history::HistoryDatabase* db) {
-    *error_info_ = work_.Run();
+    *error_ = work_.Run();
     done_->Signal();
     return true;
   }
@@ -35,7 +35,7 @@ class WorkerTask : public HistoryDBTask {
  protected:
   WorkCallback work_;
   WaitableEvent* done_;
-  UnrecoverableErrorInfo* error_info_;
+  SyncerError* error_;
 };
 
 
@@ -47,14 +47,14 @@ HistoryModelWorker::HistoryModelWorker(HistoryService* history_service)
 HistoryModelWorker::~HistoryModelWorker() {
 }
 
-UnrecoverableErrorInfo HistoryModelWorker::DoWorkAndWaitUntilDone(
+SyncerError HistoryModelWorker::DoWorkAndWaitUntilDone(
     const WorkCallback& work) {
   WaitableEvent done(false, false);
-  UnrecoverableErrorInfo error_info;
-  scoped_refptr<WorkerTask> task(new WorkerTask(work, &done, &error_info));
+  SyncerError error = UNSET;
+  scoped_refptr<WorkerTask> task(new WorkerTask(work, &done, &error));
   history_service_->ScheduleDBTask(task.get(), &cancelable_consumer_);
   done.Wait();
-  return error_info;
+  return error;
 }
 
 ModelSafeGroup HistoryModelWorker::GetModelSafeGroup() {
diff --git a/chrome/browser/sync/glue/history_model_worker.h b/chrome/browser/sync/glue/history_model_worker.h
index 108038a..9dc81b5 100644
--- a/chrome/browser/sync/glue/history_model_worker.h
+++ b/chrome/browser/sync/glue/history_model_worker.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -7,7 +7,6 @@
 #pragma once
 
 #include "chrome/browser/sync/engine/model_safe_worker.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
 
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
@@ -27,7 +26,7 @@ class HistoryModelWorker : public browser_sync::ModelSafeWorker {
   virtual ~HistoryModelWorker();
 
   // ModelSafeWorker implementation. Called on syncapi SyncerThread.
-  virtual UnrecoverableErrorInfo DoWorkAndWaitUntilDone(
+  virtual SyncerError DoWorkAndWaitUntilDone(
       const WorkCallback& work) OVERRIDE;
   virtual ModelSafeGroup GetModelSafeGroup() OVERRIDE;
 
diff --git a/chrome/browser/sync/glue/password_model_worker.cc b/chrome/browser/sync/glue/password_model_worker.cc
index 826cf21..84c95e4 100644
--- a/chrome/browser/sync/glue/password_model_worker.cc
+++ b/chrome/browser/sync/glue/password_model_worker.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -20,22 +20,22 @@ PasswordModelWorker::PasswordModelWorker(PasswordStore* password_store)
 
 PasswordModelWorker::~PasswordModelWorker() {}
 
-UnrecoverableErrorInfo PasswordModelWorker::DoWorkAndWaitUntilDone(
+SyncerError PasswordModelWorker::DoWorkAndWaitUntilDone(
     const WorkCallback& work) {
   WaitableEvent done(false, false);
-  UnrecoverableErrorInfo error_info;
+  SyncerError error = UNSET;
   password_store_->ScheduleTask(
       base::Bind(&PasswordModelWorker::CallDoWorkAndSignalTask,
-                 this, work, &done, &error_info));
+                 this, work, &done, &error));
   done.Wait();
-  return error_info;
+  return error;
 }
 
 void PasswordModelWorker::CallDoWorkAndSignalTask(
     const WorkCallback& work,
     WaitableEvent* done,
-    UnrecoverableErrorInfo* error_info) {
-  *error_info = work.Run();
+    SyncerError *error) {
+  *error = work.Run();
   done->Signal();
 }
 
diff --git a/chrome/browser/sync/glue/password_model_worker.h b/chrome/browser/sync/glue/password_model_worker.h
index 6e6c76e..92740c7 100644
--- a/chrome/browser/sync/glue/password_model_worker.h
+++ b/chrome/browser/sync/glue/password_model_worker.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -7,7 +7,6 @@
 #pragma once
 
 #include "chrome/browser/sync/engine/model_safe_worker.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
 
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
@@ -31,7 +30,7 @@ class PasswordModelWorker : public browser_sync::ModelSafeWorker {
   virtual ~PasswordModelWorker();
 
   // ModelSafeWorker implementation. Called on syncapi SyncerThread.
-  virtual UnrecoverableErrorInfo DoWorkAndWaitUntilDone(
+  virtual SyncerError DoWorkAndWaitUntilDone(
       const WorkCallback& work) OVERRIDE;
   virtual ModelSafeGroup GetModelSafeGroup() OVERRIDE;
 
@@ -39,7 +38,7 @@ class PasswordModelWorker : public browser_sync::ModelSafeWorker {
   void CallDoWorkAndSignalTask(
     const WorkCallback& work,
     base::WaitableEvent* done,
-    UnrecoverableErrorInfo* error_info);
+    SyncerError* error);
 
   scoped_refptr<PasswordStore> password_store_;
   DISALLOW_COPY_AND_ASSIGN(PasswordModelWorker);
diff --git a/chrome/browser/sync/glue/ui_model_worker.cc b/chrome/browser/sync/glue/ui_model_worker.cc
index 754f625..096693d 100644
--- a/chrome/browser/sync/glue/ui_model_worker.cc
+++ b/chrome/browser/sync/glue/ui_model_worker.cc
@@ -21,7 +21,7 @@ namespace {
 void CallDoWorkAndSignalCallback(const WorkCallback& work,
                                  base::WaitableEvent* work_done,
                                  UIModelWorker* const scheduler,
-                                 UnrecoverableErrorInfo* error_info) {
+                                 SyncerError* error_info) {
   if (work.is_null()) {
     // This can happen during tests or cases where there are more than just the
     // default UIModelWorker in existence and it gets destroyed before
@@ -44,7 +44,7 @@ void CallDoWorkAndSignalCallback(const WorkCallback& work,
 
 }  // namespace
 
-UnrecoverableErrorInfo UIModelWorker::DoWorkAndWaitUntilDone(
+SyncerError UIModelWorker::DoWorkAndWaitUntilDone(
     const WorkCallback& work) {
   // In most cases, this method is called in WORKING state. It is possible this
   // gets called when we are in the RUNNING_MANUAL_SHUTDOWN_PUMP state, because
@@ -53,7 +53,7 @@ UnrecoverableErrorInfo UIModelWorker::DoWorkAndWaitUntilDone(
   // code handling this case in Stop(). Note there _no_ way we can be in here
   // with state_ = STOPPED, so it is safe to read / compare in this case.
   CHECK_NE(ANNOTATE_UNPROTECTED_READ(state_), STOPPED);
-  UnrecoverableErrorInfo error_info;
+  SyncerError error_info;
   if (BrowserThread::CurrentlyOn(BrowserThread::UI)) {
     DLOG(WARNING) << "DoWorkAndWaitUntilDone called from "
       << "ui_loop_. Probably a nested invocation?";
diff --git a/chrome/browser/sync/glue/ui_model_worker.h b/chrome/browser/sync/glue/ui_model_worker.h
index 6592570..5d012ba 100644
--- a/chrome/browser/sync/glue/ui_model_worker.h
+++ b/chrome/browser/sync/glue/ui_model_worker.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -37,7 +37,7 @@ class UIModelWorker : public browser_sync::ModelSafeWorker {
   void Stop();
 
   // ModelSafeWorker implementation. Called on syncapi SyncerThread.
-  virtual UnrecoverableErrorInfo DoWorkAndWaitUntilDone(
+  virtual SyncerError DoWorkAndWaitUntilDone(
       const WorkCallback& work) OVERRIDE;
   virtual ModelSafeGroup GetModelSafeGroup() OVERRIDE;
 
diff --git a/chrome/browser/sync/glue/ui_model_worker_unittest.cc b/chrome/browser/sync/glue/ui_model_worker_unittest.cc
index 577447e..2a3db64 100644
--- a/chrome/browser/sync/glue/ui_model_worker_unittest.cc
+++ b/chrome/browser/sync/glue/ui_model_worker_unittest.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -11,12 +11,11 @@
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/thread.h"
 #include "chrome/browser/sync/glue/ui_model_worker.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
 #include "content/test/test_browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using browser_sync::UIModelWorker;
-using browser_sync::UnrecoverableErrorInfo;
+using browser_sync::SyncerError;
 using content::BrowserThread;
 
 // Various boilerplate, primarily for the StopWithPendingWork test.
@@ -29,12 +28,12 @@ class UIModelWorkerVisitor {
        was_run_(was_run) { }
   virtual ~UIModelWorkerVisitor() { }
 
-  virtual UnrecoverableErrorInfo DoWork() {
+  virtual SyncerError DoWork() {
     EXPECT_TRUE(BrowserThread::CurrentlyOn(BrowserThread::UI));
     was_run_->Signal();
     if (quit_loop_when_run_)
       MessageLoop::current()->Quit();
-    return UnrecoverableErrorInfo();
+    return browser_sync::SYNCER_OK;
   }
 
  private:
diff --git a/chrome/browser/sync/internal_api/includes/syncer_error.cc b/chrome/browser/sync/internal_api/includes/syncer_error.cc
new file mode 100644
index 0000000..5355a3b
--- /dev/null
+++ b/chrome/browser/sync/internal_api/includes/syncer_error.cc
@@ -0,0 +1,36 @@
+// Copyright (c) 2012 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.
+
+#include "chrome/browser/sync/internal_api/includes/syncer_error.h"
+
+#include "base/logging.h"
+
+namespace browser_sync {
+
+#define ENUM_CASE(x) case x: return #x; break;
+const char* GetSyncerErrorString(SyncerError value) {
+  switch (value) {
+    ENUM_CASE(UNSET);
+    ENUM_CASE(DIRECTORY_LOOKUP_FAILED);
+    ENUM_CASE(NETWORK_CONNECTION_UNAVAILABLE);
+    ENUM_CASE(NETWORK_IO_ERROR);
+    ENUM_CASE(SYNC_SERVER_ERROR);
+    ENUM_CASE(SYNC_AUTH_ERROR);
+    ENUM_CASE(SERVER_RETURN_INVALID_CREDENTIAL);
+    ENUM_CASE(SERVER_RETURN_UNKNOWN_ERROR);
+    ENUM_CASE(SERVER_RETURN_THROTTLED);
+    ENUM_CASE(SERVER_RETURN_TRANSIENT_ERROR);
+    ENUM_CASE(SERVER_RETURN_MIGRATION_DONE);
+    ENUM_CASE(SERVER_RETURN_CLEAR_PENDING);
+    ENUM_CASE(SERVER_RETURN_NOT_MY_BIRTHDAY);
+    ENUM_CASE(SERVER_RESPONSE_VALIDATION_FAILED);
+    ENUM_CASE(SYNCER_OK);
+  }
+  NOTREACHED();
+  return "INVALID";
+}
+#undef ENUM_CASE
+
+} // namespace browser_sync
+
diff --git a/chrome/browser/sync/internal_api/includes/syncer_error.h b/chrome/browser/sync/internal_api/includes/syncer_error.h
new file mode 100644
index 0000000..1f3c03b
--- /dev/null
+++ b/chrome/browser/sync/internal_api/includes/syncer_error.h
@@ -0,0 +1,46 @@
+// Copyright (c) 2012 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.
+
+#ifndef CHROME_BROWSER_SYNC_INTERNAL_API_INCLUDES_SYNCER_ERROR_H_
+#define CHROME_BROWSER_SYNC_INTERNAL_API_INCLUDES_SYNCER_ERROR_H_
+#pragma once
+
+namespace browser_sync {
+
+// This enum describes all the ways a SyncerCommand can fail.
+//
+// SyncerCommands do many different things, but they share a common function
+// signature.  This enum, the return value for all SyncerCommands, must be able
+// to describe any possible failure for all SyncerComand.
+//
+// For convenience, functions which are invoked only by SyncerCommands may also
+// return a SyncerError.  It saves us having to write a conversion function, and
+// it makes refactoring easier.
+enum SyncerError {
+  UNSET = 0,       // Default value.
+  DIRECTORY_LOOKUP_FAILED, // Local directory lookup failure.
+
+  NETWORK_CONNECTION_UNAVAILABLE,  // Connectivity failure.
+  NETWORK_IO_ERROR,                // Response buffer read error.
+  SYNC_SERVER_ERROR,               // Non auth HTTP error.
+  SYNC_AUTH_ERROR,                 // HTTP auth error.
+
+  // Based on values returned by server.  Most are defined in sync.proto.
+  SERVER_RETURN_INVALID_CREDENTIAL,
+  SERVER_RETURN_UNKNOWN_ERROR,
+  SERVER_RETURN_THROTTLED,
+  SERVER_RETURN_TRANSIENT_ERROR,
+  SERVER_RETURN_MIGRATION_DONE,
+  SERVER_RETURN_CLEAR_PENDING,
+  SERVER_RETURN_NOT_MY_BIRTHDAY,
+  SERVER_RESPONSE_VALIDATION_FAILED,
+
+  SYNCER_OK
+};
+
+const char * GetSyncerErrorString(SyncerError);
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_INTERNAL_API_INCLUDES_SYNCER_ERROR_H_
diff --git a/chrome/browser/sync/test/engine/fake_model_worker.cc b/chrome/browser/sync/test/engine/fake_model_worker.cc
index 0599350..5b3dc60 100644
--- a/chrome/browser/sync/test/engine/fake_model_worker.cc
+++ b/chrome/browser/sync/test/engine/fake_model_worker.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -16,7 +16,7 @@ FakeModelWorker::~FakeModelWorker() {
   DCHECK(non_thread_safe_.CalledOnValidThread());
 }
 
-UnrecoverableErrorInfo FakeModelWorker::DoWorkAndWaitUntilDone(
+SyncerError FakeModelWorker::DoWorkAndWaitUntilDone(
     const WorkCallback& work) {
   DCHECK(non_thread_safe_.CalledOnValidThread());
   // Simply do the work on the current thread.
diff --git a/chrome/browser/sync/test/engine/fake_model_worker.h b/chrome/browser/sync/test/engine/fake_model_worker.h
index 28e340b..e80a2cd 100644
--- a/chrome/browser/sync/test/engine/fake_model_worker.h
+++ b/chrome/browser/sync/test/engine/fake_model_worker.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -12,6 +12,7 @@
 #include "base/compiler_specific.h"
 #include "base/threading/non_thread_safe.h"
 #include "chrome/browser/sync/engine/model_safe_worker.h"
+#include "chrome/browser/sync/internal_api/includes/syncer_error.h"
 
 namespace browser_sync {
 
@@ -22,7 +23,7 @@ class FakeModelWorker : public ModelSafeWorker {
   explicit FakeModelWorker(ModelSafeGroup group);
 
   // ModelSafeWorker implementation.
-  virtual UnrecoverableErrorInfo DoWorkAndWaitUntilDone(
+  virtual SyncerError DoWorkAndWaitUntilDone(
       const WorkCallback& work) OVERRIDE;
   virtual ModelSafeGroup GetModelSafeGroup() OVERRIDE;
 
diff --git a/chrome/chrome.gyp b/chrome/chrome.gyp
index 650cfab..59db3d397c 100644
--- a/chrome/chrome.gyp
+++ b/chrome/chrome.gyp
@@ -1,4 +1,4 @@
-# Copyright (c) 2011 The Chromium Authors. All rights reserved.
+# Copyright (c) 2012 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.
 {
@@ -262,6 +262,8 @@
       'sources': [
         'browser/sync/engine/syncapi_internal.cc',
         'browser/sync/engine/syncapi_internal.h',
+        'browser/sync/internal_api/includes/syncer_error.cc',
+        'browser/sync/internal_api/includes/syncer_error.h',
         'browser/sync/internal_api/includes/unrecoverable_error_handler.h',
         'browser/sync/internal_api/base_node.cc',
         'browser/sync/internal_api/base_node.h',