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

chrome/browser/chrome_browser_main.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/browser/chrome_browser_main.h"
 
 #if defined(TOOLKIT_GTK)
 #include <gtk/gtk.h>
 #endif
 
@@ skipping 1312 matching lines @@
 
   // TODO(stevenjb): Move WIN and MACOSX specific code to appropriate Parts.
   // (requires supporting early exit).
   PostProfileInit();
 
   // Retrieve cached GL strings from local state and use them for GPU
   // blacklist decisions.
   if (g_browser_process->gl_string_manager())
     g_browser_process->gl_string_manager()->Initialize();
 
+  // Create an instance of GpuModeManager to watch gpu mode pref change.
+  g_browser_process->gpu_mode_manager();
+
 #if !defined(OS_ANDROID)
   // Show the First Run UI if this is the first time Chrome has been run on
   // this computer, or we're being compelled to do so by a command line flag.
   // Note that this be done _after_ the PrefService is initialized and all
   // preferences are registered, since some of the code that the importer
   // touches reads preferences.
   if (do_first_run_tasks_) {
     first_run::AutoImport(profile_,
                           master_prefs_->homepage_defined,
                           master_prefs_->do_import_items,
@@ skipping 468 matching lines @@
     if (base::win::GetVersion() <= base::win::VERSION_XP)
       uma_name += "_XP";
 
     uma_name += "_PreRead_";
     uma_name += pre_read_percentage;
     AddPreReadHistogramTime(uma_name.c_str(), time);
   }
 #endif
 #endif
 }