Add Statistics for SupervisedUserSettingService during merging and syncing data.

chrome/browser/supervised_user/legacy/supervised_user_shared_settings_service.cc

 // Copyright 2014 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/supervised_user/legacy/supervised_user_shared_settings_service.h"
 
 #include <map>
 #include <set>
 #include <utility>
 
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
+#include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
 #include "base/values.h"
 #include "chrome/common/pref_names.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "sync/api/sync_change.h"
 #include "sync/api/sync_data.h"
 #include "sync/api/sync_error.h"
 #include "sync/api/sync_error_factory.h"
 #include "sync/api/sync_merge_result.h"
@@ skipping 229 matching lines @@
     }
   }
 
   SyncMergeResult result(SUPERVISED_USER_SHARED_SETTINGS);
   // Process all the accumulated changes.
   if (change_list.size() > 0) {
     result.set_error(
         sync_processor_->ProcessSyncChanges(FROM_HERE, change_list));
   }
 
-  // TODO(bauerb): Statistics?

[Bernhard Bauer, 2016/01/04 12:53:30]

Sorry, that comment should have been more detailed 😃 The statistics mentioned
here are statistics about the merge result, i.e. things like the number of items
that were added, deleted, updated, etc. (see the API of SyncMergeResult for
details), not UMA histograms.

[Deepak, 2016/01/05 03:45:16]

Done.

+  UMA_HISTOGRAM_ENUMERATION("SupervisedUserSettingService.SyncMergeResult",
+                            result.model_type(), syncer::MODEL_TYPE_COUNT);
+
   return result;
 }
 
 void SupervisedUserSharedSettingsService::StopSyncing(syncer::ModelType type) {
   DCHECK_EQ(SUPERVISED_USER_SHARED_SETTINGS, type);
   sync_processor_.reset();
   error_handler_.reset();
 }
 
 syncer::SyncDataList SupervisedUserSharedSettingsService::GetAllSyncData(
@@ skipping 64 matching lines @@
         NOTREACHED();
         break;
       }
     }
     callbacks_.Notify(su_id, key);
   }
 
   SyncError error;
   return error;
 }