Add UMA data for memory pressure warning received for sync

components/sync_driver/pref_names.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 "components/sync_driver/pref_names.h"
 
 namespace sync_driver {
 
 namespace prefs {
 
@@ skipping 83 matching lines @@
 const char kSyncRemainingRollbackTries[] = "sync.remaining_rollback_tries";
 
 // Stores the timestamp of first sync.
 const char kSyncFirstSyncTime[] = "sync.first_sync_time";
 
 // Stores whether a platform specific passphrase error prompt has been shown to
 // the user (e.g. an Android system notification). Used for out of band prompts
 // that we only want to use once.
 const char kSyncPassphrasePrompted[] = "sync.passphrase_prompted";
 
+// Stores how many times received MEMORY_PRESSURE_LEVEL_CRITICAL
+const char kSyncMemoryPressureReceivings[] = "sync.memory_warning_receivings";
+
+// Stores if sync shutdown correctly (not crash)
+const char kSyncShutdownUnnormal[] = "sync.shutdown_forced";
+
 }  // namespace prefs
 
 }  // namespace sync_driver