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

chrome/browser/prefs/browser_prefs.cc

Index: chrome/browser/prefs/browser_prefs.cc
===================================================================
--- chrome/browser/prefs/browser_prefs.cc	(revision 186737)
+++ chrome/browser/prefs/browser_prefs.cc	(working copy)
@@ -33,6 +33,7 @@
 #include "chrome/browser/google/google_url_tracker.h"
 #include "chrome/browser/google/google_url_tracker_factory.h"
 #include "chrome/browser/gpu/gl_string_manager.h"
+#include "chrome/browser/gpu/gpu_mode_manager.h"
 #include "chrome/browser/intranet_redirect_detector.h"
 #include "chrome/browser/io_thread.h"
 #include "chrome/browser/managed_mode/managed_mode.h"
@@ -183,6 +184,7 @@
   FlagsUI::RegisterPrefs(registry);
   geolocation::RegisterPrefs(registry);
   GLStringManager::RegisterPrefs(registry);
+  GpuModeManager::RegisterPrefs(registry);
   IntranetRedirectDetector::RegisterPrefs(registry);
   IOThread::RegisterPrefs(registry);
   KeywordEditorController::RegisterPrefs(registry);