[Sync] Have MergeDataAndStartSyncing return a SyncMergeResult

This will allow us to track merge statistics for datatypes. For now none of
the datatypes fill the SyncMergeResult with anything other than an error.

BUG=158576
TBR=stevet@chromium.org

Review URL: https://chromiumcodereview.appspot.com/11365241

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@168446 0039d316-1c4b-4281-b951-d872f2087c98

31 files changed, 143 insertions, 108 deletions

diff --git a/chrome/browser/extensions/app_notification_manager.cc b/chrome/browser/extensions/app_notification_manager.cc
index 2dbaaf4..2d8cfcf 100644
--- a/chrome/browser/extensions/app_notification_manager.cc
+++ b/chrome/browser/extensions/app_notification_manager.cc
@@ -285,12 +285,13 @@ syncer::SyncError AppNotificationManager::ProcessSyncChanges(
   return error;
 }
 
-syncer::SyncError AppNotificationManager::MergeDataAndStartSyncing(
+syncer::SyncMergeResult AppNotificationManager::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
     scoped_ptr<syncer::SyncErrorFactory> sync_error_factory) {
   CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  syncer::SyncMergeResult merge_result(type);
   // AppNotificationDataTypeController ensures that modei is fully should before
   // this method is called by waiting until the load notification is received
   // from AppNotificationManager.
@@ -324,10 +325,11 @@ syncer::SyncError AppNotificationManager::MergeDataAndStartSyncing(
       // Local notification should always match with sync notification as
       // notifications are immutable.
       if (local_notif->is_local() || !sync_notif->Equals(*local_notif)) {
-        return sync_error_factory_->CreateAndUploadError(
+        merge_result.set_error(sync_error_factory_->CreateAndUploadError(
              FROM_HERE,
             "MergeDataAndStartSyncing failed: local notification and sync "
-            "notification have same guid but different data.");
+            "notification have same guid but different data."));
+        return merge_result;
       }
     } else {
       // Sync model has a notification that local model does not, add it.
@@ -345,11 +347,12 @@ syncer::SyncError AppNotificationManager::MergeDataAndStartSyncing(
                            iter->second));
   }
 
-  syncer::SyncError error;
-  if (new_changes.size() > 0)
-    error = sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes);
-  models_associated_ = !error.IsSet();
-  return error;
+  if (new_changes.size() > 0) {
+    merge_result.set_error(
+        sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes));
+  }
+  models_associated_ = !merge_result.error().IsSet();
+  return merge_result;
 }
 
 void AppNotificationManager::StopSyncing(syncer::ModelType type) {
diff --git a/chrome/browser/extensions/app_notification_manager.h b/chrome/browser/extensions/app_notification_manager.h
index 71a1ba0..405b349 100644
--- a/chrome/browser/extensions/app_notification_manager.h
+++ b/chrome/browser/extensions/app_notification_manager.h
@@ -76,7 +76,7 @@ class AppNotificationManager
       const tracked_objects::Location& from_here,
       const syncer::SyncChangeList& change_list) OVERRIDE;
   // Associate and merge sync data model with our data model.
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/chrome/browser/extensions/app_notification_manager_sync_unittest.cc b/chrome/browser/extensions/app_notification_manager_sync_unittest.cc
index b761c58..f1e79f1 100644
--- a/chrome/browser/extensions/app_notification_manager_sync_unittest.cc
+++ b/chrome/browser/extensions/app_notification_manager_sync_unittest.cc
@@ -479,7 +479,7 @@ TEST_F(AppNotificationManagerSyncTest, ModelAssocBothNonEmptyTitleMismatch) {
       syncer::APP_NOTIFICATIONS,
       initial_data,
       PassProcessor(),
-      error_handler.PassAs<syncer::SyncErrorFactory>());
+      error_handler.PassAs<syncer::SyncErrorFactory>()).error();
 
   EXPECT_TRUE(sync_error.IsSet());
   EXPECT_EQ(syncer::APP_NOTIFICATIONS, sync_error.type());
@@ -512,7 +512,7 @@ TEST_F(AppNotificationManagerSyncTest, ModelAssocBothNonEmptyMatchesLocal) {
       syncer::APP_NOTIFICATIONS,
       initial_data,
       PassProcessor(),
-      error_handler.PassAs<syncer::SyncErrorFactory>());
+      error_handler.PassAs<syncer::SyncErrorFactory>()).error();
 
   EXPECT_TRUE(sync_error.IsSet());
   EXPECT_EQ(syncer::APP_NOTIFICATIONS, sync_error.type());
diff --git a/chrome/browser/extensions/extension_service.cc b/chrome/browser/extensions/extension_service.cc
index 503dd2e..872a9ee 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -1287,7 +1287,7 @@ void ExtensionService::CheckForUpdatesSoon() {
   }
 }
 
-syncer::SyncError ExtensionService::MergeDataAndStartSyncing(
+syncer::SyncMergeResult ExtensionService::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
@@ -1340,7 +1340,7 @@ syncer::SyncError ExtensionService::MergeDataAndStartSyncing(
     app_sync_bundle_.ProcessSyncChangeList(sync_change_list);
   }
 
-  return syncer::SyncError();
+  return syncer::SyncMergeResult(type);
 }
 
 void ExtensionService::StopSyncing(syncer::ModelType type) {
diff --git a/chrome/browser/extensions/extension_service.h b/chrome/browser/extensions/extension_service.h
index 7fa2eb1..4f8d737 100644
--- a/chrome/browser/extensions/extension_service.h
+++ b/chrome/browser/extensions/extension_service.h
@@ -461,7 +461,7 @@ class ExtensionService
   virtual void CheckForUpdatesSoon() OVERRIDE;
 
   // syncer::SyncableService implementation.
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/chrome/browser/extensions/settings/settings_apitest.cc b/chrome/browser/extensions/settings/settings_apitest.cc
index cbcbca8..2232e8b 100644
--- a/chrome/browser/extensions/settings/settings_apitest.cc
+++ b/chrome/browser/extensions/settings/settings_apitest.cc
@@ -207,7 +207,7 @@ class ExtensionSettingsApiTest : public ExtensionApiTest {
         scoped_ptr<syncer::SyncChangeProcessor>(
             new SyncChangeProcessorDelegate(sync_processor)),
         scoped_ptr<syncer::SyncErrorFactory>(
-            new syncer::SyncErrorFactoryMock())).IsSet());
+            new syncer::SyncErrorFactoryMock())).error().IsSet());
   }
 
   void SendChangesToSyncableService(
diff --git a/chrome/browser/extensions/settings/settings_backend.cc b/chrome/browser/extensions/settings/settings_backend.cc
index 988a564..37b635bf 100644
--- a/chrome/browser/extensions/settings/settings_backend.cc
+++ b/chrome/browser/extensions/settings/settings_backend.cc
@@ -168,7 +168,7 @@ syncer::SyncDataList SettingsBackend::GetAllSyncData(
   return all_sync_data;
 }
 
-syncer::SyncError SettingsBackend::MergeDataAndStartSyncing(
+syncer::SyncMergeResult SettingsBackend::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
@@ -231,7 +231,7 @@ syncer::SyncError SettingsBackend::MergeDataAndStartSyncing(
     GetOrCreateStorageWithSyncData(it->first, *it->second);
   }
 
-  return syncer::SyncError();
+  return syncer::SyncMergeResult(type);
 }
 
 syncer::SyncError SettingsBackend::ProcessSyncChanges(
diff --git a/chrome/browser/extensions/settings/settings_backend.h b/chrome/browser/extensions/settings/settings_backend.h
index 95c6428..3a3bab5 100644
--- a/chrome/browser/extensions/settings/settings_backend.h
+++ b/chrome/browser/extensions/settings/settings_backend.h
@@ -50,7 +50,7 @@ class SettingsBackend : public syncer::SyncableService {
   // syncer::SyncableService implementation.
   virtual syncer::SyncDataList GetAllSyncData(
       syncer::ModelType type) const OVERRIDE;
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/chrome/browser/extensions/test_extension_service.cc b/chrome/browser/extensions/test_extension_service.cc
index 8ab1122..8dfedfb 100644
--- a/chrome/browser/extensions/test_extension_service.cc
+++ b/chrome/browser/extensions/test_extension_service.cc
@@ -79,13 +79,13 @@ void TestExtensionService::CheckForUpdatesSoon() {
   ADD_FAILURE();
 }
 
-syncer::SyncError TestExtensionService::MergeDataAndStartSyncing(
+syncer::SyncMergeResult TestExtensionService::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
     scoped_ptr<syncer::SyncErrorFactory> sync_error_factory) {
   ADD_FAILURE();
-  return syncer::SyncError();
+  return syncer::SyncMergeResult(type);
 }
 
 void TestExtensionService::StopSyncing(syncer::ModelType type) {
diff --git a/chrome/browser/extensions/test_extension_service.h b/chrome/browser/extensions/test_extension_service.h
index d4dbb87..0121dab 100644
--- a/chrome/browser/extensions/test_extension_service.h
+++ b/chrome/browser/extensions/test_extension_service.h
@@ -52,7 +52,7 @@ class TestExtensionService : public ExtensionServiceInterface {
   virtual void CheckManagementPolicy() OVERRIDE;
   virtual void CheckForUpdatesSoon() OVERRIDE;
 
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/chrome/browser/history/history.cc b/chrome/browser/history/history.cc
index 3591e5c..01a0a57 100644
--- a/chrome/browser/history/history.cc
+++ b/chrome/browser/history/history.cc
@@ -915,7 +915,7 @@ base::WeakPtr<HistoryService> HistoryService::AsWeakPtr() {
   return weak_ptr_factory_.GetWeakPtr();
 }
 
-syncer::SyncError HistoryService::MergeDataAndStartSyncing(
+syncer::SyncMergeResult HistoryService::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
@@ -927,7 +927,7 @@ syncer::SyncError HistoryService::MergeDataAndStartSyncing(
     DCHECK_EQ(it->GetDataType(), syncer::HISTORY_DELETE_DIRECTIVES);
     ProcessDeleteDirective(it->GetSpecifics().history_delete_directive());
   }
-  return syncer::SyncError();
+  return syncer::SyncMergeResult(type);
 }
 
 void HistoryService::StopSyncing(syncer::ModelType type) {
diff --git a/chrome/browser/history/history.h b/chrome/browser/history/history.h
index 6c5cf34..494f19a 100644
--- a/chrome/browser/history/history.h
+++ b/chrome/browser/history/history.h
@@ -633,7 +633,7 @@ class HistoryService : public CancelableRequestProvider,
   base::WeakPtr<HistoryService> AsWeakPtr();
 
   // syncer::SyncableService implementation.
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/chrome/browser/prefs/pref_model_associator.cc b/chrome/browser/prefs/pref_model_associator.cc
index 894f607..0b3c119 100644
--- a/chrome/browser/prefs/pref_model_associator.cc
+++ b/chrome/browser/prefs/pref_model_associator.cc
@@ -110,7 +110,7 @@ void PrefModelAssociator::InitPrefAndAssociate(
   return;
 }
 
-syncer::SyncError PrefModelAssociator::MergeDataAndStartSyncing(
+syncer::SyncMergeResult PrefModelAssociator::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
@@ -121,6 +121,7 @@ syncer::SyncError PrefModelAssociator::MergeDataAndStartSyncing(
   DCHECK(!sync_processor_.get());
   DCHECK(sync_processor.get());
   DCHECK(sync_error_factory.get());
+  syncer::SyncMergeResult merge_result(type);
   sync_processor_ = sync_processor.Pass();
   sync_error_factory_ = sync_error_factory.Pass();
 
@@ -157,15 +158,14 @@ syncer::SyncError PrefModelAssociator::MergeDataAndStartSyncing(
   }
 
   // Push updates to sync.
-  syncer::SyncError error =
-      sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes);
-  if (error.IsSet()) {
-    return error;
-  }
+  merge_result.set_error(
+      sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes));
+  if (merge_result.error().IsSet())
+    return merge_result;
 
   models_associated_ = true;
   pref_service_->OnIsSyncingChanged();
-  return syncer::SyncError();
+  return merge_result;
 }
 
 void PrefModelAssociator::StopSyncing(syncer::ModelType type) {
diff --git a/chrome/browser/prefs/pref_model_associator.h b/chrome/browser/prefs/pref_model_associator.h
index a5cfbdd..aaeeded 100644
--- a/chrome/browser/prefs/pref_model_associator.h
+++ b/chrome/browser/prefs/pref_model_associator.h
@@ -43,7 +43,7 @@ class PrefModelAssociator
   virtual syncer::SyncError ProcessSyncChanges(
       const tracked_objects::Location& from_here,
       const syncer::SyncChangeList& change_list) OVERRIDE;
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/chrome/browser/search_engines/template_url_service.cc b/chrome/browser/search_engines/template_url_service.cc
index 381811a..e10e5b8 100644
--- a/chrome/browser/search_engines/template_url_service.cc
+++ b/chrome/browser/search_engines/template_url_service.cc
@@ -1110,7 +1110,7 @@ syncer::SyncError TemplateURLService::ProcessSyncChanges(
   return error;
 }
 
-syncer::SyncError TemplateURLService::MergeDataAndStartSyncing(
+syncer::SyncMergeResult TemplateURLService::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
@@ -1120,6 +1120,7 @@ syncer::SyncError TemplateURLService::MergeDataAndStartSyncing(
   DCHECK(!sync_processor_.get());
   DCHECK(sync_processor.get());
   DCHECK(sync_error_factory.get());
+  syncer::SyncMergeResult merge_result(type);
   sync_processor_ = sync_processor.Pass();
   sync_error_factory_ = sync_error_factory.Pass();
 
@@ -1233,17 +1234,17 @@ syncer::SyncError TemplateURLService::MergeDataAndStartSyncing(
 
   LogDuplicatesHistogram(GetTemplateURLs());
 
-  syncer::SyncError error =
-      sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes);
-  if (error.IsSet())
-    return error;
+  merge_result.set_error(
+      sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes));
+  if (merge_result.error().IsSet())
+    return merge_result;
 
   // The ACTION_DELETEs from this set are processed. Empty it so we don't try to
   // reuse them on the next call to MergeDataAndStartSyncing.
   pre_sync_deletes_.clear();
 
   models_associated_ = true;
-  return syncer::SyncError();
+  return merge_result;
 }
 
 void TemplateURLService::StopSyncing(syncer::ModelType type) {
diff --git a/chrome/browser/search_engines/template_url_service.h b/chrome/browser/search_engines/template_url_service.h
index 510f11c..eea98e3 100644
--- a/chrome/browser/search_engines/template_url_service.h
+++ b/chrome/browser/search_engines/template_url_service.h
@@ -286,7 +286,7 @@ class TemplateURLService : public WebDataServiceConsumer,
   // Merge initial search engine data from Sync and push any local changes up
   // to Sync. This may send notifications if local search engines are added,
   // updated or removed.
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/chrome/browser/search_engines/template_url_service_sync_unittest.cc b/chrome/browser/search_engines/template_url_service_sync_unittest.cc
index 5ba4974..223cda6 100644
--- a/chrome/browser/search_engines/template_url_service_sync_unittest.cc
+++ b/chrome/browser/search_engines/template_url_service_sync_unittest.cc
@@ -1276,9 +1276,11 @@ TEST_F(TemplateURLServiceSyncTest, MergeTwoClientsDupesAndConflicts) {
 
 TEST_F(TemplateURLServiceSyncTest, StopSyncing) {
   syncer::SyncError error =
-      model()->MergeDataAndStartSyncing(syncer::SEARCH_ENGINES,
-      CreateInitialSyncData(), PassProcessor(),
-      CreateAndPassSyncErrorFactory());
+      model()->MergeDataAndStartSyncing(
+          syncer::SEARCH_ENGINES,
+          CreateInitialSyncData(),
+          PassProcessor(),
+          CreateAndPassSyncErrorFactory()).error();
   ASSERT_FALSE(error.IsSet());
   model()->StopSyncing(syncer::SEARCH_ENGINES);
 
@@ -1297,9 +1299,11 @@ TEST_F(TemplateURLServiceSyncTest, StopSyncing) {
 TEST_F(TemplateURLServiceSyncTest, SyncErrorOnInitialSync) {
   processor()->set_erroneous(true);
   syncer::SyncError error =
-      model()->MergeDataAndStartSyncing(syncer::SEARCH_ENGINES,
-      CreateInitialSyncData(), PassProcessor(),
-      CreateAndPassSyncErrorFactory());
+      model()->MergeDataAndStartSyncing(
+          syncer::SEARCH_ENGINES,
+          CreateInitialSyncData(),
+          PassProcessor(),
+          CreateAndPassSyncErrorFactory()).error();
   EXPECT_TRUE(error.IsSet());
 
   // Ensure that if the initial merge was erroneous, then subsequence attempts
@@ -1322,9 +1326,11 @@ TEST_F(TemplateURLServiceSyncTest, SyncErrorOnLaterSync) {
   // Ensure that if the SyncProcessor succeeds in the initial merge, but fails
   // in future ProcessSyncChanges, we still return an error.
   syncer::SyncError error =
-      model()->MergeDataAndStartSyncing(syncer::SEARCH_ENGINES,
-      CreateInitialSyncData(), PassProcessor(),
-      CreateAndPassSyncErrorFactory());
+      model()->MergeDataAndStartSyncing(
+          syncer::SEARCH_ENGINES,
+          CreateInitialSyncData(),
+          PassProcessor(),
+          CreateAndPassSyncErrorFactory()).error();
   ASSERT_FALSE(error.IsSet());
 
   syncer::SyncChangeList changes;
@@ -1346,8 +1352,11 @@ TEST_F(TemplateURLServiceSyncTest, MergeTwiceWithSameSyncData) {
                                      "key1", 10));  // earlier
 
   syncer::SyncError error =
-      model()->MergeDataAndStartSyncing(syncer::SEARCH_ENGINES,
-      initial_data, PassProcessor(), CreateAndPassSyncErrorFactory());
+      model()->MergeDataAndStartSyncing(
+          syncer::SEARCH_ENGINES,
+          initial_data,
+          PassProcessor(),
+          CreateAndPassSyncErrorFactory()).error();
   ASSERT_FALSE(error.IsSet());
 
   // We should have updated the original TemplateURL with Sync's version.
@@ -1373,8 +1382,11 @@ TEST_F(TemplateURLServiceSyncTest, MergeTwiceWithSameSyncData) {
   model()->StopSyncing(syncer::SEARCH_ENGINES);
   sync_processor_delegate_.reset(new SyncChangeProcessorDelegate(
       sync_processor_.get()));
-  error = model()->MergeDataAndStartSyncing(syncer::SEARCH_ENGINES,
-      initial_data, PassProcessor(), CreateAndPassSyncErrorFactory());
+  error = model()->MergeDataAndStartSyncing(
+      syncer::SEARCH_ENGINES,
+      initial_data,
+      PassProcessor(),
+      CreateAndPassSyncErrorFactory()).error();
   ASSERT_FALSE(error.IsSet());
 
   // Check that the TemplateURL was not modified.
diff --git a/chrome/browser/sync/glue/new_non_frontend_data_type_controller.cc b/chrome/browser/sync/glue/new_non_frontend_data_type_controller.cc
index f510c99..f352b79 100644
--- a/chrome/browser/sync/glue/new_non_frontend_data_type_controller.cc
+++ b/chrome/browser/sync/glue/new_non_frontend_data_type_controller.cc
@@ -285,7 +285,7 @@ void NewNonFrontendDataTypeController::
   // TODO(zea): Call shared_change_processor_->GetAllSyncData(..) before
   // and after MergeDataAndStartSyncing and store the item counts into
   // syncer_merge_result.
-  error =
+  local_merge_result =
       local_service_->MergeDataAndStartSyncing(
           type(),
           initial_sync_data,
@@ -294,8 +294,7 @@ void NewNonFrontendDataTypeController::
           scoped_ptr<syncer::SyncErrorFactory>(
               new SharedChangeProcessorRef(shared_change_processor)));
   RecordAssociationTime(base::TimeTicks::Now() - start_time);
-  if (error.IsSet()) {
-    local_merge_result.set_error(error);
+  if (local_merge_result.error().IsSet()) {
     StartDone(ASSOCIATION_FAILED,
               local_merge_result,
               syncer_merge_result);
diff --git a/chrome/browser/sync/glue/ui_data_type_controller.cc b/chrome/browser/sync/glue/ui_data_type_controller.cc
index 51fbf2d..797e4a4 100644
--- a/chrome/browser/sync/glue/ui_data_type_controller.cc
+++ b/chrome/browser/sync/glue/ui_data_type_controller.cc
@@ -170,12 +170,8 @@ void UIDataTypeController::Associate() {
   }
 
   // Passes a reference to |shared_change_processor_|.
-  // TODO(zea): have SyncableService return a SyncMergeResult and pass that on
-  // to the ModelAssociationManager.
-  // TODO(zea): Call shared_change_processor_->GetAllSyncData(..) before
-  // and after MergeDataAndStartSyncing and store the item counts into
-  // syncer_merge_result.
-  error = local_service_->MergeDataAndStartSyncing(
+  syncer_merge_result.set_num_items_after_association(initial_sync_data.size());
+  local_merge_result = local_service_->MergeDataAndStartSyncing(
       type(),
       initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor>(
@@ -183,8 +179,8 @@ void UIDataTypeController::Associate() {
       scoped_ptr<syncer::SyncErrorFactory>(
           new SharedChangeProcessorRef(shared_change_processor_)));
   RecordAssociationTime(base::TimeTicks::Now() - start_time);
-  if (error.IsSet()) {
-    local_merge_result.set_error(error);
+
+  if (local_merge_result.error().IsSet()) {
     StartDone(ASSOCIATION_FAILED,
               local_merge_result,
               syncer_merge_result);
diff --git a/chrome/browser/themes/theme_syncable_service.cc b/chrome/browser/themes/theme_syncable_service.cc
index 063347e..5b969d2 100644
--- a/chrome/browser/themes/theme_syncable_service.cc
+++ b/chrome/browser/themes/theme_syncable_service.cc
@@ -56,7 +56,7 @@ void ThemeSyncableService::OnThemeChange() {
   }
 }
 
-syncer::SyncError ThemeSyncableService::MergeDataAndStartSyncing(
+syncer::SyncMergeResult ThemeSyncableService::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
@@ -66,6 +66,7 @@ syncer::SyncError ThemeSyncableService::MergeDataAndStartSyncing(
   DCHECK(sync_processor.get());
   DCHECK(error_handler.get());
 
+  syncer::SyncMergeResult merge_result(type);
   sync_processor_ = sync_processor.Pass();
   sync_error_handler_ = error_handler.Pass();
 
@@ -86,12 +87,14 @@ syncer::SyncError ThemeSyncableService::MergeDataAndStartSyncing(
       ++sync_data) {
     if (sync_data->GetSpecifics().has_theme()) {
       MaybeSetTheme(current_specifics, *sync_data);
-      return syncer::SyncError();
+      return merge_result;
     }
   }
 
   // No theme specifics are found. Create one according to current theme.
-  return ProcessNewTheme(syncer::SyncChange::ACTION_ADD, current_specifics);
+  merge_result.set_error(ProcessNewTheme(
+      syncer::SyncChange::ACTION_ADD, current_specifics));
+  return merge_result;
 }
 
 void ThemeSyncableService::StopSyncing(syncer::ModelType type) {
diff --git a/chrome/browser/themes/theme_syncable_service.h b/chrome/browser/themes/theme_syncable_service.h
index 0ce64c0..408fd0e 100644
--- a/chrome/browser/themes/theme_syncable_service.h
+++ b/chrome/browser/themes/theme_syncable_service.h
@@ -33,7 +33,7 @@ class ThemeSyncableService : public syncer::SyncableService {
   void OnThemeChange();
 
   // syncer::SyncableService implementation.
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/chrome/browser/themes/theme_syncable_service_unittest.cc b/chrome/browser/themes/theme_syncable_service_unittest.cc
index e7f9a2d..e82369a 100644
--- a/chrome/browser/themes/theme_syncable_service_unittest.cc
+++ b/chrome/browser/themes/theme_syncable_service_unittest.cc
@@ -277,7 +277,8 @@ TEST_F(ThemeSyncableServiceTest, SetCurrentThemeDefaultTheme) {
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(sync_pb::ThemeSpecifics()),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_FALSE(error.IsSet()) << error.message();
   EXPECT_TRUE(fake_theme_service_->UsingDefaultTheme());
 }
@@ -291,7 +292,8 @@ TEST_F(ThemeSyncableServiceTest, SetCurrentThemeSystemTheme) {
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(theme_specifics),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_FALSE(error.IsSet()) << error.message();
   EXPECT_TRUE(fake_theme_service_->UsingNativeTheme());
 }
@@ -308,7 +310,8 @@ TEST_F(ThemeSyncableServiceTest, SetCurrentThemeCustomTheme) {
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(theme_specifics),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_FALSE(error.IsSet()) << error.message();
   EXPECT_EQ(fake_theme_service_->theme_extension(), theme_extension_.get());
 }
@@ -320,7 +323,8 @@ TEST_F(ThemeSyncableServiceTest, DontResetThemeWhenSpecificsAreEqual) {
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(sync_pb::ThemeSpecifics()),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_FALSE(error.IsSet()) << error.message();
   EXPECT_FALSE(fake_theme_service_->is_dirty());
 }
@@ -335,7 +339,8 @@ TEST_F(ThemeSyncableServiceTest, UpdateThemeSpecificsFromCurrentTheme) {
 
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, syncer::SyncDataList(), fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_FALSE(error.IsSet()) << error.message();
 
   ASSERT_EQ(1u, change_list.size());
@@ -378,7 +383,8 @@ TEST_F(ThemeSyncableServiceTest, ProcessSyncThemeChange) {
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(sync_pb::ThemeSpecifics()),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_FALSE(error.IsSet()) << error.message();
   // Don't expect theme change initially because specifics are equal.
   EXPECT_FALSE(fake_theme_service_->is_dirty());
@@ -413,7 +419,8 @@ TEST_F(ThemeSyncableServiceTest, OnThemeChangeByUser) {
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(sync_pb::ThemeSpecifics()),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_FALSE(error.IsSet()) << error.message();
   EXPECT_EQ(0u, change_list.size());
 
@@ -442,7 +449,8 @@ TEST_F(ThemeSyncableServiceTest, StopSync) {
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(sync_pb::ThemeSpecifics()),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_FALSE(error.IsSet()) << error.message();
   EXPECT_EQ(0u, change_list.size());
 
@@ -475,7 +483,8 @@ TEST_F(ThemeSyncableServiceTest, RestoreSystemThemeBitWhenChangeToCustomTheme) {
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(theme_specifics),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
 
   // Change to custom theme and notify theme_sync_service_.
   // use_system_theme_by_default bit should be preserved.
@@ -502,7 +511,8 @@ TEST_F(ThemeSyncableServiceTest,
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(theme_specifics),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_FALSE(fake_theme_service_->is_dirty());
 
   // Change to default theme and notify theme_sync_service_.
@@ -544,7 +554,8 @@ TEST_F(ThemeSyncableServiceTest,
   syncer::SyncError error = theme_sync_service_->MergeDataAndStartSyncing(
       syncer::THEMES, MakeThemeDataList(theme_specifics),
       fake_change_processor_.Pass(),
-      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock()));
+      scoped_ptr<syncer::SyncErrorFactory>(new syncer::SyncErrorFactoryMock())).
+          error();
   EXPECT_EQ(fake_theme_service_->theme_extension(), theme_extension_.get());
 
   // Change to default theme and notify theme_sync_service_.
diff --git a/chrome/browser/webdata/autocomplete_syncable_service.cc b/chrome/browser/webdata/autocomplete_syncable_service.cc
index 451ebfe..b583be1 100644
--- a/chrome/browser/webdata/autocomplete_syncable_service.cc
+++ b/chrome/browser/webdata/autocomplete_syncable_service.cc
@@ -115,7 +115,7 @@ AutocompleteSyncableService::AutocompleteSyncableService()
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
 }
 
-syncer::SyncError AutocompleteSyncableService::MergeDataAndStartSyncing(
+syncer::SyncMergeResult AutocompleteSyncableService::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
@@ -126,12 +126,14 @@ syncer::SyncError AutocompleteSyncableService::MergeDataAndStartSyncing(
   DCHECK(error_handler.get());
   VLOG(1) << "Associating Autocomplete: MergeDataAndStartSyncing";
 
+  syncer::SyncMergeResult merge_result(type);
   error_handler_ = error_handler.Pass();
   std::vector<AutofillEntry> entries;
   if (!LoadAutofillData(&entries)) {
-    return error_handler_->CreateAndUploadError(
+    merge_result.set_error(error_handler_->CreateAndUploadError(
         FROM_HERE,
-        "Could not get the autocomplete data from WebDatabase.");
+        "Could not get the autocomplete data from WebDatabase."));
+    return merge_result;
   }
 
   AutocompleteEntryMap new_db_entries;
@@ -154,9 +156,10 @@ syncer::SyncError AutocompleteSyncableService::MergeDataAndStartSyncing(
   }
 
   if (!SaveChangesToWebData(new_synced_entries)) {
-    return error_handler_->CreateAndUploadError(
+    merge_result.set_error(error_handler_->CreateAndUploadError(
         FROM_HERE,
-        "Failed to update webdata.");
+        "Failed to update webdata."));
+    return merge_result;
   }
 
   WebDataService::NotifyOfMultipleAutofillChanges(web_data_service_);
@@ -176,10 +179,9 @@ syncer::SyncError AutocompleteSyncableService::MergeDataAndStartSyncing(
     web_data_service_->RemoveExpiredFormElements();
   }
 
-  syncer::SyncError error =
-      sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes);
-
-  return error;
+  merge_result.set_error(
+      sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes));
+  return merge_result;
 }
 
 void AutocompleteSyncableService::StopSyncing(syncer::ModelType type) {
diff --git a/chrome/browser/webdata/autocomplete_syncable_service.h b/chrome/browser/webdata/autocomplete_syncable_service.h
index caa3439..e543955 100644
--- a/chrome/browser/webdata/autocomplete_syncable_service.h
+++ b/chrome/browser/webdata/autocomplete_syncable_service.h
@@ -50,7 +50,7 @@ class AutocompleteSyncableService
   static syncer::ModelType model_type() { return syncer::AUTOFILL; }
 
   // syncer::SyncableService implementation.
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/chrome/browser/webdata/autofill_profile_syncable_service.cc b/chrome/browser/webdata/autofill_profile_syncable_service.cc
index 334edf4..e2c8e9d 100644
--- a/chrome/browser/webdata/autofill_profile_syncable_service.cc
+++ b/chrome/browser/webdata/autofill_profile_syncable_service.cc
@@ -57,7 +57,8 @@ AutofillProfileSyncableService::AutofillProfileSyncableService()
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
 }
 
-syncer::SyncError AutofillProfileSyncableService::MergeDataAndStartSyncing(
+syncer::SyncMergeResult
+AutofillProfileSyncableService::MergeDataAndStartSyncing(
     syncer::ModelType type,
     const syncer::SyncDataList& initial_sync_data,
     scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
@@ -68,10 +69,12 @@ syncer::SyncError AutofillProfileSyncableService::MergeDataAndStartSyncing(
   DCHECK(sync_error_factory.get());
   DVLOG(1) << "Associating Autofill: MergeDataAndStartSyncing";
 
+  syncer::SyncMergeResult merge_result(type);
   sync_error_factory_ = sync_error_factory.Pass();
   if (!LoadAutofillData(&profiles_.get())) {
-    return sync_error_factory_->CreateAndUploadError(
-        FROM_HERE, "Could not get the autofill data from WebDatabase.");
+    merge_result.set_error(sync_error_factory_->CreateAndUploadError(
+        FROM_HERE, "Could not get the autofill data from WebDatabase."));
+    return merge_result;
   }
 
   if (DLOG_IS_ON(INFO)) {
@@ -131,9 +134,10 @@ syncer::SyncError AutofillProfileSyncableService::MergeDataAndStartSyncing(
   }
 
   if (!SaveChangesToWebData(bundle)) {
-    return sync_error_factory_->CreateAndUploadError(
+    merge_result.set_error(sync_error_factory_->CreateAndUploadError(
         FROM_HERE,
-        "Failed to update webdata.");
+        "Failed to update webdata."));
+    return merge_result;
   }
 
   syncer::SyncChangeList new_changes;
@@ -153,13 +157,14 @@ syncer::SyncError AutofillProfileSyncableService::MergeDataAndStartSyncing(
                            CreateData(*(bundle.profiles_to_sync_back[i]))));
   }
 
-  syncer::SyncError error;
-  if (!new_changes.empty())
-    error = sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes);
+  if (!new_changes.empty()) {
+    merge_result.set_error(
+        sync_processor_->ProcessSyncChanges(FROM_HERE, new_changes));
+  }
 
   WebDataService::NotifyOfMultipleAutofillChanges(web_data_service_);
 
-  return error;
+  return merge_result;
 }
 
 void AutofillProfileSyncableService::StopSyncing(syncer::ModelType type) {
diff --git a/chrome/browser/webdata/autofill_profile_syncable_service.h b/chrome/browser/webdata/autofill_profile_syncable_service.h
index 10af923..44c88cf 100644
--- a/chrome/browser/webdata/autofill_profile_syncable_service.h
+++ b/chrome/browser/webdata/autofill_profile_syncable_service.h
@@ -47,7 +47,7 @@ class AutofillProfileSyncableService
   static syncer::ModelType model_type() { return syncer::AUTOFILL_PROFILE; }
 
   // syncer::SyncableService implementation.
-  virtual syncer::SyncError MergeDataAndStartSyncing(
+  virtual syncer::SyncMergeResult MergeDataAndStartSyncing(
       syncer::ModelType type,
       const syncer::SyncDataList& initial_sync_data,
       scoped_ptr<syncer::SyncChangeProcessor> sync_processor,
diff --git a/sync/api/fake_syncable_service.cc b/sync/api/fake_syncable_service.cc
index 731b24d..0d76f2e 100644
--- a/sync/api/fake_syncable_service.cc
+++ b/sync/api/fake_syncable_service.cc
@@ -30,17 +30,20 @@ bool FakeSyncableService::syncing() const {
 }
 
 // SyncableService implementation.
-SyncError FakeSyncableService::MergeDataAndStartSyncing(
+SyncMergeResult FakeSyncableService::MergeDataAndStartSyncing(
     ModelType type,
     const SyncDataList& initial_sync_data,
     scoped_ptr<SyncChangeProcessor> sync_processor,
     scoped_ptr<SyncErrorFactory> sync_error_factory) {
+  SyncMergeResult merge_result(type);
   sync_processor_ = sync_processor.Pass();
   type_ = type;
   if (!merge_data_and_start_syncing_error_.IsSet()) {
     syncing_ = true;
+  } else {
+    merge_result.set_error(merge_data_and_start_syncing_error_);
   }
-  return merge_data_and_start_syncing_error_;
+  return merge_result;
 }
 
 void FakeSyncableService::StopSyncing(ModelType type) {
diff --git a/sync/api/fake_syncable_service.h b/sync/api/fake_syncable_service.h
index 5a501ae..3d77a80 100644
--- a/sync/api/fake_syncable_service.h
+++ b/sync/api/fake_syncable_service.h
@@ -27,7 +27,7 @@ class FakeSyncableService : public SyncableService {
   bool syncing() const;
 
   // SyncableService implementation.
-  virtual SyncError MergeDataAndStartSyncing(
+  virtual SyncMergeResult MergeDataAndStartSyncing(
       ModelType type,
       const SyncDataList& initial_sync_data,
       scoped_ptr<SyncChangeProcessor> sync_processor,
diff --git a/sync/api/sync_merge_result.cc b/sync/api/sync_merge_result.cc
index c2253b3..0caf57b 100644
--- a/sync/api/sync_merge_result.cc
+++ b/sync/api/sync_merge_result.cc
@@ -20,7 +20,7 @@ SyncMergeResult::~SyncMergeResult() {
 
 // Setters.
 void SyncMergeResult::set_error(SyncError error) {
-  DCHECK_EQ(model_type_, error.type());
+  DCHECK(!error.IsSet() || model_type_ == error.type());
   error_ = error;
 }
 
diff --git a/sync/api/sync_merge_result.h b/sync/api/sync_merge_result.h
index 41accfd..baa4eb4 100644
--- a/sync/api/sync_merge_result.h
+++ b/sync/api/sync_merge_result.h
@@ -26,8 +26,7 @@ class SyncMergeResult {
   // Default copy and assign welcome.
 
   // Setters.
-  // Note: |error.IsSet()| must be true, and |error.type()| must match
-  // model_type_
+  // Note: if |error.IsSet()| is true, |error.type()| must match model_type_
   void set_error(SyncError error);
   void set_num_items_before_association(int num_items_before_association);
   void set_num_items_after_association(int num_items_after_association);
diff --git a/sync/api/syncable_service.h b/sync/api/syncable_service.h
index 5f84d85..571c2e7 100644
--- a/sync/api/syncable_service.h
+++ b/sync/api/syncable_service.h
@@ -13,6 +13,7 @@
 #include "sync/api/sync_change_processor.h"
 #include "sync/api/sync_data.h"
 #include "sync/api/sync_error.h"
+#include "sync/api/sync_merge_result.h"
 #include "sync/internal_api/public/base/model_type.h"
 
 namespace syncer {
@@ -33,10 +34,10 @@ class SyncableService : public SyncChangeProcessor,
   // two. After this, the SyncableService's local data should match the server
   // data, and the service should be ready to receive and process any further
   // SyncChange's as they occur.
-  // Returns: A default SyncError (IsSet() == false) if no errors were
-  //          encountered, and a filled SyncError (IsSet() == true)
-  //          otherwise.
-  virtual SyncError MergeDataAndStartSyncing(
+  // Returns: a SyncMergeResult whose error field reflects whether an error
+  //          was encountered while merging the two models. The merge result
+  //          may also contain optional merge statistics.
+  virtual SyncMergeResult MergeDataAndStartSyncing(
       ModelType type,
       const SyncDataList& initial_sync_data,
       scoped_ptr<SyncChangeProcessor> sync_processor,