Add UMA stats for GPU feature disable checkbox.

chrome/common/pref_names.h

 // Copyright (c) 2012 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.
 
 // Constants for the names of various preferences, for easier changing.
 
 #ifndef CHROME_COMMON_PREF_NAMES_H_
 #define CHROME_COMMON_PREF_NAMES_H_
 
 #include <stddef.h>
@@ skipping 770 matching lines @@
 #endif
 
 extern const char kRegisteredProtocolHandlers[];
 extern const char kIgnoredProtocolHandlers[];
 extern const char kCustomHandlersEnabled[];
 
 extern const char kUserCreatedLoginItem[];
 extern const char kUserRemovedLoginItem[];
 extern const char kBackgroundModeEnabled[];
 extern const char kHardwareAccelerationModeEnabled[];
+extern const char kHardwareAccelerationModePrevious[];
 
 extern const char kDevicePolicyRefreshRate[];
 extern const char kUserPolicyRefreshRate[];
 extern const char kDisableCloudPolicyOnSignin[];
 
 extern const char kFactoryResetRequested[];
 
 extern const char kRecoveryComponentVersion[];
 extern const char kComponentUpdaterState[];
 
@@ skipping 81 matching lines @@
 extern const char kAppListProfile[];
 
 extern const char kLastAppListLaunchPing[];
 extern const char kAppListLaunchCount[];
 extern const char kLastAppListAppLaunchPing[];
 extern const char kAppListAppLaunchCount[];
 
 }  // namespace prefs
 
 #endif  // CHROME_COMMON_PREF_NAMES_H_