Add a user pref in Settings to disable all GPU features.

chrome/test/base/testing_browser_process.cc

 // 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.
 
 #include "chrome/test/base/testing_browser_process.h"
 
 #include "base/prefs/pref_service.h"
 #include "base/string_util.h"
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 118 matching lines @@
 }
 
 IconManager* TestingBrowserProcess::icon_manager() {
   return NULL;
 }
 
 GLStringManager* TestingBrowserProcess::gl_string_manager() {
   return NULL;
 }
 
+GpuModeManager* TestingBrowserProcess::gpu_mode_manager() {
+  return NULL;
+}
+
 RenderWidgetSnapshotTaker*
 TestingBrowserProcess::GetRenderWidgetSnapshotTaker() {
 #if defined(OS_IOS)
   NOTREACHED();
   return NULL;
 #else
   return render_widget_snapshot_taker_.get();
 #endif
 }
 
@@ skipping 233 matching lines @@
 #endif
 }
 
 void TestingBrowserProcess::SetSafeBrowsingService(
     SafeBrowsingService* sb_service) {
 #if !defined(OS_IOS)
   NOTIMPLEMENTED();
   sb_service_ = sb_service;
 #endif
 }