[Sync] Move some code into new class JsMutationEventObserver

Move JsTransactionObserver code into JsMutationEventObserver.

Move ChangeObserver methods of JsSyncManagerObserver to
JsMutationEventObserver.

BUG=
TEST=

Review URL: http://codereview.chromium.org/7982049

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@102414 0039d316-1c4b-4281-b951-d872f2087c98

11 files changed, 213 insertions, 173 deletions

diff --git a/chrome/browser/resources/sync_internals/chrome_sync.js b/chrome/browser/resources/sync_internals/chrome_sync.js
index 62b2f6a..aeef59f 100644
--- a/chrome/browser/resources/sync_internals/chrome_sync.js
+++ b/chrome/browser/resources/sync_internals/chrome_sync.js
@@ -91,7 +91,7 @@ chrome.sync.events = {
 
   'transaction': [
     'onTransactionStart',
-    'onTransactionMutate',
+    'onTransactionWrite',
     'onTransactionEnd'
   ]
 };
diff --git a/chrome/browser/sync/internal_api/sync_manager.cc b/chrome/browser/sync/internal_api/sync_manager.cc
index e2f1c2f..5e1c537 100644
--- a/chrome/browser/sync/internal_api/sync_manager.cc
+++ b/chrome/browser/sync/internal_api/sync_manager.cc
@@ -34,9 +34,9 @@
 #include "chrome/browser/sync/js/js_backend.h"
 #include "chrome/browser/sync/js/js_event_details.h"
 #include "chrome/browser/sync/js/js_event_handler.h"
+#include "chrome/browser/sync/js/js_mutation_event_observer.h"
 #include "chrome/browser/sync/js/js_reply_handler.h"
 #include "chrome/browser/sync/js/js_sync_manager_observer.h"
-#include "chrome/browser/sync/js/js_transaction_observer.h"
 #include "chrome/browser/sync/notifier/sync_notifier.h"
 #include "chrome/browser/sync/notifier/sync_notifier_observer.h"
 #include "chrome/browser/sync/protocol/proto_value_conversions.h"
@@ -61,8 +61,8 @@ using browser_sync::JsEventDetails;
 using browser_sync::JsEventHandler;
 using browser_sync::JsEventHandler;
 using browser_sync::JsReplyHandler;
+using browser_sync::JsMutationEventObserver;
 using browser_sync::JsSyncManagerObserver;
-using browser_sync::JsTransactionObserver;
 using browser_sync::ModelSafeWorkerRegistrar;
 using browser_sync::kNigoriTag;
 using browser_sync::KeyParams;
@@ -549,7 +549,7 @@ class SyncManager::SyncInternal
   JsMessageHandlerMap js_message_handlers_;
   WeakHandle<JsEventHandler> js_event_handler_;
   JsSyncManagerObserver js_sync_manager_observer_;
-  JsTransactionObserver js_transaction_observer_;
+  JsMutationEventObserver js_mutation_event_observer_;
 };
 const int SyncManager::SyncInternal::kDefaultNudgeDelayMilliseconds = 200;
 const int SyncManager::SyncInternal::kPreferencesNudgeDelayMilliseconds = 2000;
@@ -756,7 +756,6 @@ bool SyncManager::SyncInternal::Init(
 
   sync_notifier_.reset(sync_notifier);
 
-  AddChangeObserver(&js_sync_manager_observer_);
   AddObserver(&js_sync_manager_observer_);
   SetJsEventHandler(event_handler);
 
@@ -897,7 +896,8 @@ bool SyncManager::SyncInternal::OpenDirectory() {
   }
 
   connection_manager()->set_client_id(lookup->cache_guid());
-  lookup->AddTransactionObserver(&js_transaction_observer_);
+  lookup->AddTransactionObserver(&js_mutation_event_observer_);
+  AddChangeObserver(&js_mutation_event_observer_);
   return true;
 }
 
@@ -1262,7 +1262,6 @@ void SyncManager::SyncInternal::Shutdown() {
   scheduler_.reset();
 
   SetJsEventHandler(WeakHandle<JsEventHandler>());
-  RemoveChangeObserver(&js_sync_manager_observer_);
   RemoveObserver(&js_sync_manager_observer_);
 
   if (sync_notifier_.get()) {
@@ -1281,7 +1280,8 @@ void SyncManager::SyncInternal::Shutdown() {
   if (dir_manager()) {
     syncable::ScopedDirLookup lookup(dir_manager(), username_for_share());
     if (lookup.good()) {
-      lookup->RemoveTransactionObserver(&js_transaction_observer_);
+      lookup->RemoveTransactionObserver(&js_mutation_event_observer_);
+      RemoveChangeObserver(&js_mutation_event_observer_);
     } else {
       NOTREACHED();
     }
@@ -1680,7 +1680,7 @@ void SyncManager::SyncInternal::SetJsEventHandler(
     const WeakHandle<JsEventHandler>& event_handler) {
   js_event_handler_ = event_handler;
   js_sync_manager_observer_.SetJsEventHandler(js_event_handler_);
-  js_transaction_observer_.SetJsEventHandler(js_event_handler_);
+  js_mutation_event_observer_.SetJsEventHandler(js_event_handler_);
 }
 
 void SyncManager::SyncInternal::ProcessJsMessage(
diff --git a/chrome/browser/sync/js/js_transaction_observer.cc b/chrome/browser/sync/js/js_mutation_event_observer.cc
index e271336..5087a23 100644
--- a/chrome/browser/sync/js/js_transaction_observer.cc
+++ b/chrome/browser/sync/js/js_mutation_event_observer.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chrome/browser/sync/js/js_transaction_observer.h"
+#include "chrome/browser/sync/js/js_mutation_event_observer.h"
 
 #include <string>
 
@@ -15,18 +15,18 @@
 
 namespace browser_sync {
 
-JsTransactionObserver::JsTransactionObserver() {}
+JsMutationEventObserver::JsMutationEventObserver() {}
 
-JsTransactionObserver::~JsTransactionObserver() {
+JsMutationEventObserver::~JsMutationEventObserver() {
   DCHECK(non_thread_safe_.CalledOnValidThread());
 }
 
-void JsTransactionObserver::SetJsEventHandler(
+void JsMutationEventObserver::SetJsEventHandler(
     const WeakHandle<JsEventHandler>& event_handler) {
   event_handler_ = event_handler;
 }
 
-void JsTransactionObserver::OnTransactionStart(
+void JsMutationEventObserver::OnTransactionStart(
     const tracked_objects::Location& location,
     const syncable::WriterTag& writer) {
   DCHECK(non_thread_safe_.CalledOnValidThread());
@@ -41,13 +41,53 @@ void JsTransactionObserver::OnTransactionStart(
 
 namespace {
 
-// Max number of mutations we attempt to convert to values (to avoid
+// Max number of changes we attempt to convert to values (to avoid
 // running out of memory).
-const size_t kMutationLimit = 300;
+const size_t kChangeLimit = 100;
 
 }  // namespace
 
-void JsTransactionObserver::OnTransactionWrite(
+void JsMutationEventObserver::OnChangesApplied(
+    syncable::ModelType model_type,
+    int64 write_transaction_id,
+    const sync_api::ImmutableChangeRecordList& changes) {
+  if (!event_handler_.IsInitialized()) {
+    return;
+  }
+  DictionaryValue details;
+  details.SetString("modelType", syncable::ModelTypeToString(model_type));
+  details.SetString("writeTransactionId",
+                    base::Int64ToString(write_transaction_id));
+  base::Value* changes_value = NULL;
+  const size_t changes_size = changes.Get().size();
+  if (changes_size <= kChangeLimit) {
+    ListValue* changes_list = new ListValue();
+    for (sync_api::ChangeRecordList::const_iterator it =
+             changes.Get().begin(); it != changes.Get().end(); ++it) {
+      changes_list->Append(it->ToValue());
+    }
+    changes_value = changes_list;
+  } else {
+    changes_value =
+        Value::CreateStringValue(
+            base::Uint64ToString(static_cast<uint64>(changes_size)) +
+            " changes");
+  }
+  details.Set("changes", changes_value);
+  HandleJsEvent(FROM_HERE, "onChangesApplied", JsEventDetails(&details));
+}
+
+void JsMutationEventObserver::OnChangesComplete(
+    syncable::ModelType model_type) {
+  if (!event_handler_.IsInitialized()) {
+    return;
+  }
+  DictionaryValue details;
+  details.SetString("modelType", syncable::ModelTypeToString(model_type));
+  HandleJsEvent(FROM_HERE, "onChangesComplete", JsEventDetails(&details));
+}
+
+void JsMutationEventObserver::OnTransactionWrite(
     const syncable::ImmutableWriteTransactionInfo& write_transaction_info,
     const syncable::ModelTypeBitSet& models_with_changes) {
   DCHECK(non_thread_safe_.CalledOnValidThread());
@@ -56,13 +96,13 @@ void JsTransactionObserver::OnTransactionWrite(
   }
   DictionaryValue details;
   details.Set("writeTransactionInfo",
-              write_transaction_info.Get().ToValue(kMutationLimit));
+              write_transaction_info.Get().ToValue(kChangeLimit));
   details.Set("modelsWithChanges",
               syncable::ModelTypeBitSetToValue(models_with_changes));
-  HandleJsEvent(FROM_HERE, "onTransactionMutate", JsEventDetails(&details));
+  HandleJsEvent(FROM_HERE, "onTransactionWrite", JsEventDetails(&details));
 }
 
-void JsTransactionObserver::OnTransactionEnd(
+void JsMutationEventObserver::OnTransactionEnd(
     const tracked_objects::Location& location,
     const syncable::WriterTag& writer) {
   DCHECK(non_thread_safe_.CalledOnValidThread());
@@ -75,7 +115,7 @@ void JsTransactionObserver::OnTransactionEnd(
   HandleJsEvent(FROM_HERE, "onTransactionEnd", JsEventDetails(&details));
 }
 
-void JsTransactionObserver::HandleJsEvent(
+void JsMutationEventObserver::HandleJsEvent(
     const tracked_objects::Location& from_here,
     const std::string& name, const JsEventDetails& details) {
   if (!event_handler_.IsInitialized()) {
diff --git a/chrome/browser/sync/js/js_transaction_observer.h b/chrome/browser/sync/js/js_mutation_event_observer.h
index e9ae228..ced1d91 100644
--- a/chrome/browser/sync/js/js_transaction_observer.h
+++ b/chrome/browser/sync/js/js_mutation_event_observer.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CHROME_BROWSER_SYNC_JS_JS_TRANSACTION_OBSERVER_H_
-#define CHROME_BROWSER_SYNC_JS_JS_TRANSACTION_OBSERVER_H_
+#ifndef CHROME_BROWSER_SYNC_JS_JS_MUTATION_EVENT_OBSERVER_H_
+#define CHROME_BROWSER_SYNC_JS_JS_MUTATION_EVENT_OBSERVER_H_
 #pragma once
 
 #include <string>
@@ -11,6 +11,7 @@
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/threading/non_thread_safe.h"
+#include "chrome/browser/sync/internal_api/sync_manager.h"
 #include "chrome/browser/sync/syncable/transaction_observer.h"
 #include "chrome/browser/sync/util/weak_handle.h"
 
@@ -23,15 +24,25 @@ namespace browser_sync {
 class JsEventDetails;
 class JsEventHandler;
 
-// Routes SyncManager events to a JsEventHandler.
-class JsTransactionObserver : public syncable::TransactionObserver {
+// Observes all change- and transaction-related events and routes a
+// summarized version to a JsEventHandler.
+class JsMutationEventObserver
+    : public sync_api::SyncManager::ChangeObserver,
+      public syncable::TransactionObserver {
  public:
-  JsTransactionObserver();
+  JsMutationEventObserver();
 
-  virtual ~JsTransactionObserver();
+  virtual ~JsMutationEventObserver();
 
   void SetJsEventHandler(const WeakHandle<JsEventHandler>& event_handler);
 
+  // sync_api::SyncManager::ChangeObserver implementation.
+  virtual void OnChangesApplied(
+      syncable::ModelType model_type,
+      int64 write_transaction_id,
+      const sync_api::ImmutableChangeRecordList& changes) OVERRIDE;
+  virtual void OnChangesComplete(syncable::ModelType model_type) OVERRIDE;
+
   // syncable::TransactionObserver implementation.
   virtual void OnTransactionStart(
       const tracked_objects::Location& location,
@@ -51,9 +62,9 @@ class JsTransactionObserver : public syncable::TransactionObserver {
     const tracked_objects::Location& from_here,
     const std::string& name, const JsEventDetails& details);
 
-  DISALLOW_COPY_AND_ASSIGN(JsTransactionObserver);
+  DISALLOW_COPY_AND_ASSIGN(JsMutationEventObserver);
 };
 
 }  // namespace browser_sync
 
-#endif  // CHROME_BROWSER_SYNC_JS_JS_TRANSACTION_OBSERVER_H_
+#endif  // CHROME_BROWSER_SYNC_JS_JS_MUTATION_EVENT_OBSERVER_H_
diff --git a/chrome/browser/sync/js/js_mutation_event_observer_unittest.cc b/chrome/browser/sync/js/js_mutation_event_observer_unittest.cc
new file mode 100644
index 0000000..4a211f3
--- /dev/null
+++ b/chrome/browser/sync/js/js_mutation_event_observer_unittest.cc
@@ -0,0 +1,127 @@
+// Copyright (c) 2011 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/js/js_mutation_event_observer.h"
+
+#include "base/basictypes.h"
+#include "base/message_loop.h"
+#include "base/values.h"
+#include "chrome/browser/sync/js/js_event_details.h"
+#include "chrome/browser/sync/js/js_test_util.h"
+#include "chrome/browser/sync/syncable/model_type.h"
+#include "chrome/browser/sync/util/weak_handle.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace browser_sync {
+namespace {
+
+using ::testing::InSequence;
+using ::testing::StrictMock;
+
+class JsMutationEventObserverTest : public testing::Test {
+ protected:
+  JsMutationEventObserverTest() {
+    js_mutation_event_observer_.SetJsEventHandler(
+        mock_js_event_handler_.AsWeakHandle());
+  }
+
+ private:
+  // This must be destroyed after the member variables below in order
+  // for WeakHandles to be destroyed properly.
+  MessageLoop message_loop_;
+
+ protected:
+  StrictMock<MockJsEventHandler> mock_js_event_handler_;
+  JsMutationEventObserver js_mutation_event_observer_;
+
+  void PumpLoop() {
+    message_loop_.RunAllPending();
+  }
+};
+
+TEST_F(JsMutationEventObserverTest, OnChangesApplied) {
+  InSequence dummy;
+
+  // We don't test with passwords as that requires additional setup.
+
+  // Build a list of example ChangeRecords.
+  sync_api::ChangeRecord changes[syncable::MODEL_TYPE_COUNT];
+  for (int i = syncable::AUTOFILL_PROFILE;
+       i < syncable::MODEL_TYPE_COUNT; ++i) {
+    changes[i].id = i;
+    switch (i % 3) {
+      case 0:
+        changes[i].action =
+            sync_api::ChangeRecord::ACTION_ADD;
+        break;
+      case 1:
+        changes[i].action =
+            sync_api::ChangeRecord::ACTION_UPDATE;
+        break;
+      default:
+        changes[i].action =
+            sync_api::ChangeRecord::ACTION_DELETE;
+        break;
+    }
+  }
+
+  // For each i, we call OnChangesApplied() with the first arg equal
+  // to i cast to ModelType and the second argument with the changes
+  // starting from changes[i].
+
+  // Set expectations for each data type.
+  for (int i = syncable::AUTOFILL_PROFILE;
+       i < syncable::MODEL_TYPE_COUNT; ++i) {
+    const std::string& model_type_str =
+        syncable::ModelTypeToString(syncable::ModelTypeFromInt(i));
+    DictionaryValue expected_details;
+    expected_details.SetString("modelType", model_type_str);
+    expected_details.SetString("writeTransactionId", "0");
+    ListValue* expected_changes = new ListValue();
+    expected_details.Set("changes", expected_changes);
+    for (int j = i; j < syncable::MODEL_TYPE_COUNT; ++j) {
+      expected_changes->Append(changes[j].ToValue());
+    }
+    EXPECT_CALL(mock_js_event_handler_,
+                HandleJsEvent("onChangesApplied",
+                             HasDetailsAsDictionary(expected_details)));
+  }
+
+  // Fire OnChangesApplied() for each data type.
+  for (int i = syncable::AUTOFILL_PROFILE;
+       i < syncable::MODEL_TYPE_COUNT; ++i) {
+    sync_api::ChangeRecordList
+        local_changes(changes + i, changes + arraysize(changes));
+    js_mutation_event_observer_.OnChangesApplied(
+        syncable::ModelTypeFromInt(i),
+        0, sync_api::ImmutableChangeRecordList(&local_changes));
+  }
+
+  PumpLoop();
+}
+
+TEST_F(JsMutationEventObserverTest, OnChangesComplete) {
+  InSequence dummy;
+
+  for (int i = syncable::FIRST_REAL_MODEL_TYPE;
+       i < syncable::MODEL_TYPE_COUNT; ++i) {
+    DictionaryValue expected_details;
+    expected_details.SetString(
+        "modelType",
+        syncable::ModelTypeToString(syncable::ModelTypeFromInt(i)));
+    EXPECT_CALL(mock_js_event_handler_,
+                HandleJsEvent("onChangesComplete",
+                             HasDetailsAsDictionary(expected_details)));
+  }
+
+  for (int i = syncable::FIRST_REAL_MODEL_TYPE;
+       i < syncable::MODEL_TYPE_COUNT; ++i) {
+    js_mutation_event_observer_.OnChangesComplete(
+        syncable::ModelTypeFromInt(i));
+  }
+  PumpLoop();
+}
+
+}  // namespace
+}  // namespace browser_sync
diff --git a/chrome/browser/sync/js/js_sync_manager_observer.cc b/chrome/browser/sync/js/js_sync_manager_observer.cc
index 7f4a85e..7714f27 100644
--- a/chrome/browser/sync/js/js_sync_manager_observer.cc
+++ b/chrome/browser/sync/js/js_sync_manager_observer.cc
@@ -30,54 +30,6 @@ void JsSyncManagerObserver::SetJsEventHandler(
   event_handler_ = event_handler;
 }
 
-namespace {
-
-// Max number of changes we attempt to convert to values (to avoid
-// running out of memory).
-const size_t kChangeLimit = 300;
-
-}  // namespace
-
-void JsSyncManagerObserver::OnChangesApplied(
-    syncable::ModelType model_type,
-    int64 write_transaction_id,
-    const sync_api::ImmutableChangeRecordList& changes) {
-  if (!event_handler_.IsInitialized()) {
-    return;
-  }
-  DictionaryValue details;
-  details.SetString("modelType", syncable::ModelTypeToString(model_type));
-  details.SetString("writeTransactionId",
-                    base::Int64ToString(write_transaction_id));
-  Value* changes_value = NULL;
-  const size_t changes_size = changes.Get().size();
-  if (changes_size <= kChangeLimit) {
-    ListValue* changes_list = new ListValue();
-    for (sync_api::ChangeRecordList::const_iterator it =
-             changes.Get().begin(); it != changes.Get().end(); ++it) {
-      changes_list->Append(it->ToValue());
-    }
-    changes_value = changes_list;
-  } else {
-    changes_value =
-        Value::CreateStringValue(
-            base::Uint64ToString(static_cast<uint64>(changes_size)) +
-            " changes");
-  }
-  details.Set("changes", changes_value);
-  HandleJsEvent(FROM_HERE, "onChangesApplied", JsEventDetails(&details));
-}
-
-void JsSyncManagerObserver::OnChangesComplete(
-    syncable::ModelType model_type) {
-  if (!event_handler_.IsInitialized()) {
-    return;
-  }
-  DictionaryValue details;
-  details.SetString("modelType", syncable::ModelTypeToString(model_type));
-  HandleJsEvent(FROM_HERE, "onChangesComplete", JsEventDetails(&details));
-}
-
 void JsSyncManagerObserver::OnSyncCycleCompleted(
     const sessions::SyncSessionSnapshot* snapshot) {
   if (!event_handler_.IsInitialized()) {
diff --git a/chrome/browser/sync/js/js_sync_manager_observer.h b/chrome/browser/sync/js/js_sync_manager_observer.h
index d48e8f2..0fa1db3 100644
--- a/chrome/browser/sync/js/js_sync_manager_observer.h
+++ b/chrome/browser/sync/js/js_sync_manager_observer.h
@@ -24,22 +24,13 @@ class JsEventDetails;
 class JsEventHandler;
 
 // Routes SyncManager events to a JsEventHandler.
-class JsSyncManagerObserver
-    : public sync_api::SyncManager::ChangeObserver,
-      public sync_api::SyncManager::Observer {
+class JsSyncManagerObserver : public sync_api::SyncManager::Observer {
  public:
   JsSyncManagerObserver();
   virtual ~JsSyncManagerObserver();
 
   void SetJsEventHandler(const WeakHandle<JsEventHandler>& event_handler);
 
-  // sync_api::SyncManager::ChangeObserver implementation.
-  virtual void OnChangesApplied(
-      syncable::ModelType model_type,
-      int64 write_transaction_id,
-      const sync_api::ImmutableChangeRecordList& changes) OVERRIDE;
-  virtual void OnChangesComplete(syncable::ModelType model_type) OVERRIDE;
-
   // sync_api::SyncManager::Observer implementation.
   virtual void OnSyncCycleCompleted(
       const sessions::SyncSessionSnapshot* snapshot) OVERRIDE;
diff --git a/chrome/browser/sync/js/js_sync_manager_observer_unittest.cc b/chrome/browser/sync/js/js_sync_manager_observer_unittest.cc
index 776e426..aa1f0f1 100644
--- a/chrome/browser/sync/js/js_sync_manager_observer_unittest.cc
+++ b/chrome/browser/sync/js/js_sync_manager_observer_unittest.cc
@@ -8,7 +8,6 @@
 #include "base/location.h"
 #include "base/message_loop.h"
 #include "base/values.h"
-#include "chrome/browser/sync/js/js_arg_list.h"
 #include "chrome/browser/sync/js/js_event_details.h"
 #include "chrome/browser/sync/js/js_test_util.h"
 #include "chrome/browser/sync/protocol/sync_protocol_error.h"
@@ -68,27 +67,6 @@ TEST_F(JsSyncManagerObserverTest, NoArgNotifiations) {
   PumpLoop();
 }
 
-TEST_F(JsSyncManagerObserverTest, OnChangesComplete) {
-  InSequence dummy;
-
-  for (int i = syncable::FIRST_REAL_MODEL_TYPE;
-       i < syncable::MODEL_TYPE_COUNT; ++i) {
-    DictionaryValue expected_details;
-    expected_details.SetString(
-        "modelType",
-        syncable::ModelTypeToString(syncable::ModelTypeFromInt(i)));
-    EXPECT_CALL(mock_js_event_handler_,
-                HandleJsEvent("onChangesComplete",
-                             HasDetailsAsDictionary(expected_details)));
-  }
-
-  for (int i = syncable::FIRST_REAL_MODEL_TYPE;
-       i < syncable::MODEL_TYPE_COUNT; ++i) {
-    js_sync_manager_observer_.OnChangesComplete(syncable::ModelTypeFromInt(i));
-  }
-  PumpLoop();
-}
-
 TEST_F(JsSyncManagerObserverTest, OnSyncCycleCompleted) {
   std::string download_progress_markers[syncable::MODEL_TYPE_COUNT];
   sessions::SyncSessionSnapshot snapshot(sessions::SyncerStatus(),
@@ -234,66 +212,5 @@ TEST_F(JsSyncManagerObserverTest, OnEncryptionComplete) {
   PumpLoop();
 }
 
-TEST_F(JsSyncManagerObserverTest, OnChangesApplied) {
-  InSequence dummy;
-
-  // We don't test with passwords as that requires additional setup.
-
-  // Build a list of example ChangeRecords.
-  sync_api::ChangeRecord changes[syncable::MODEL_TYPE_COUNT];
-  for (int i = syncable::AUTOFILL_PROFILE;
-       i < syncable::MODEL_TYPE_COUNT; ++i) {
-    changes[i].id = i;
-    switch (i % 3) {
-      case 0:
-        changes[i].action =
-            sync_api::ChangeRecord::ACTION_ADD;
-        break;
-      case 1:
-        changes[i].action =
-            sync_api::ChangeRecord::ACTION_UPDATE;
-        break;
-      default:
-        changes[i].action =
-            sync_api::ChangeRecord::ACTION_DELETE;
-        break;
-    }
-  }
-
-  // For each i, we call OnChangesApplied() with the first arg equal
-  // to i cast to ModelType and the second argument with the changes
-  // starting from changes[i].
-
-  // Set expectations for each data type.
-  for (int i = syncable::AUTOFILL_PROFILE;
-       i < syncable::MODEL_TYPE_COUNT; ++i) {
-    const std::string& model_type_str =
-        syncable::ModelTypeToString(syncable::ModelTypeFromInt(i));
-    DictionaryValue expected_details;
-    expected_details.SetString("modelType", model_type_str);
-    expected_details.SetString("writeTransactionId", "0");
-    ListValue* expected_changes = new ListValue();
-    expected_details.Set("changes", expected_changes);
-    for (int j = i; j < syncable::MODEL_TYPE_COUNT; ++j) {
-      expected_changes->Append(changes[j].ToValue());
-    }
-    EXPECT_CALL(mock_js_event_handler_,
-                HandleJsEvent("onChangesApplied",
-                             HasDetailsAsDictionary(expected_details)));
-  }
-
-  // Fire OnChangesApplied() for each data type.
-  for (int i = syncable::AUTOFILL_PROFILE;
-       i < syncable::MODEL_TYPE_COUNT; ++i) {
-    sync_api::ChangeRecordList
-        local_changes(changes + i, changes + arraysize(changes));
-    js_sync_manager_observer_.OnChangesApplied(
-        syncable::ModelTypeFromInt(i),
-        0, sync_api::ImmutableChangeRecordList(&local_changes));
-  }
-
-  PumpLoop();
-}
-
 }  // namespace
 }  // namespace browser_sync
diff --git a/chrome/browser/sync/syncable/syncable.h b/chrome/browser/sync/syncable/syncable.h
index a3b3bcd..4f8875f 100644
--- a/chrome/browser/sync/syncable/syncable.h
+++ b/chrome/browser/sync/syncable/syncable.h
@@ -627,7 +627,8 @@ struct WriteTransactionInfo {
   base::DictionaryValue* ToValue(size_t max_mutations_size) const;
 
   int64 id;
-  // TODO(akalin): Use Location when it becomes assignable.
+  // If tracked_objects::Location becomes assignable, we can use that
+  // instead.
   std::string location_string;
   WriterTag writer;
   ImmutableEntryKernelMutationMap mutations;
diff --git a/chrome/chrome.gyp b/chrome/chrome.gyp
index d293039..646ff7e 100644
--- a/chrome/chrome.gyp
+++ b/chrome/chrome.gyp
@@ -642,10 +642,10 @@
         'browser/sync/js/js_event_details.h',
         'browser/sync/js/js_event_handler.h',
         'browser/sync/js/js_reply_handler.h',
+        'browser/sync/js/js_mutation_event_observer.cc',
+        'browser/sync/js/js_mutation_event_observer.h',
         'browser/sync/js/js_sync_manager_observer.cc',
         'browser/sync/js/js_sync_manager_observer.h',
-        'browser/sync/js/js_transaction_observer.cc',
-        'browser/sync/js/js_transaction_observer.h',
         'browser/sync/protocol/proto_enum_conversions.cc',
         'browser/sync/protocol/proto_enum_conversions.h',
         'browser/sync/protocol/proto_value_conversions.cc',
diff --git a/chrome/chrome_tests.gypi b/chrome/chrome_tests.gypi
index 9ecb3a8..029adc9 100644
--- a/chrome/chrome_tests.gypi
+++ b/chrome/chrome_tests.gypi
@@ -2931,6 +2931,7 @@
         'browser/sync/internal_api/syncapi_unittest.cc',
         'browser/sync/js/js_arg_list_unittest.cc',
         'browser/sync/js/js_event_details_unittest.cc',
+        'browser/sync/js/js_mutation_event_observer_unittest.cc',
         'browser/sync/js/js_sync_manager_observer_unittest.cc',
         'browser/sync/notifier/cache_invalidation_packet_handler_unittest.cc',
         'browser/sync/notifier/chrome_invalidation_client_unittest.cc',