[SyncFS] Add UMAs to track syncfs usage

chrome/browser/sync_file_system/drive_backend/metadata_database_index.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/sync_file_system/drive_backend/metadata_database_index.h"
 
+#include "base/metrics/histogram.h"
 #include "chrome/browser/sync_file_system/drive_backend/drive_backend_constants.h"
 #include "chrome/browser/sync_file_system/drive_backend/metadata_database.pb.h"
 
 namespace sync_file_system {
 namespace drive_backend {
 
 ParentIDAndTitle::ParentIDAndTitle() : parent_id(0) {}
 ParentIDAndTitle::ParentIDAndTitle(int64 parent_id,
                                    const std::string& title)
     : parent_id(parent_id), title(title) {}
@@ skipping 34 matching lines @@
 }  // namespace
 
 MetadataDatabaseIndex::MetadataDatabaseIndex(DatabaseContents* content) {
   for (size_t i = 0; i < content->file_metadata.size(); ++i)
     StoreFileMetadata(make_scoped_ptr(content->file_metadata[i]));
   content->file_metadata.weak_clear();
 
   for (size_t i = 0; i < content->file_trackers.size(); ++i)
     StoreFileTracker(make_scoped_ptr(content->file_trackers[i]));
   content->file_trackers.weak_clear();
+
+  UMA_HISTOGRAM_COUNTS("SyncFileSystem.MetadataNumber", metadata_by_id_.size());
+  UMA_HISTOGRAM_COUNTS("SyncFileSystem.TrackerNumber", tracker_by_id_.size());
+  UMA_HISTOGRAM_COUNTS_100("SyncFileSystem.RegisteredAppNumber",
+                           app_root_by_app_id_.size());
 }
 
 MetadataDatabaseIndex::~MetadataDatabaseIndex() {}
 
 const FileTracker* MetadataDatabaseIndex::GetFileTracker(
     int64 tracker_id) const {
   return tracker_by_id_.get(tracker_id);
 }
 
 const FileMetadata* MetadataDatabaseIndex::GetFileMetadata(
@@ skipping 389 matching lines @@
 
     DVLOG(3) << "  Remove from dirty_trackers_: " << tracker_id;
     dirty_trackers_.erase(tracker_id);
 
     demoted_dirty_trackers_.erase(tracker_id);
   }
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system