Add chromium side flag for enabling/disabling layer squashing.

content/browser/renderer_host/render_view_host_impl.cc

Index: content/browser/renderer_host/render_view_host_impl.cc
diff --git a/content/browser/renderer_host/render_view_host_impl.cc b/content/browser/renderer_host/render_view_host_impl.cc
index 2372870321e79d81ff9b0443f56cb4d30883bf4b..f54c6181a9e8031b8831526fd4d76e57873a9cab 100644
--- a/content/browser/renderer_host/render_view_host_impl.cc
+++ b/content/browser/renderer_host/render_view_host_impl.cc
@@ -374,6 +374,12 @@ WebPreferences RenderViewHostImpl::GetWebkitPrefs(const GURL& url) {
   if (command_line.HasSwitch(switches::kDisableAcceleratedOverflowScroll))
     prefs.accelerated_compositing_for_overflow_scroll_enabled = false;
 
+  prefs.layer_squashing_enabled = false;
+  if (command_line.HasSwitch(switches::kEnableLayerSquashing))
+      prefs.layer_squashing_enabled = true;
+  if (command_line.HasSwitch(switches::kDisableLayerSquashing))
+      prefs.layer_squashing_enabled = false;
+
   prefs.accelerated_compositing_for_scrollable_frames_enabled = false;
   if (command_line.HasSwitch(switches::kEnableAcceleratedScrollableFrames))
     prefs.accelerated_compositing_for_scrollable_frames_enabled = true;
@@ -426,6 +432,8 @@ WebPreferences RenderViewHostImpl::GetWebkitPrefs(const GURL& url) {
       command_line.HasSwitch(switches::kEnableExperimentalWebPlatformFeatures);
   prefs.region_based_columns_enabled =
       command_line.HasSwitch(switches::kEnableRegionBasedColumns);
+  prefs.layer_squashing_enabled =

[jochen (gone - plz use gerrit), 2013/11/20 08:59:45]

this overrides anything you've set above in line 377ff

[shawnsingh, 2013/11/20 18:08:57]

whoops - left from a previous iteration of the patch.  Thanks for catching this.

+      command_line.HasSwitch(switches::kEnableLayerSquashing);
   prefs.threaded_html_parser =
       !command_line.HasSwitch(switches::kDisableThreadedHTMLParser);
   prefs.experimental_websocket_enabled =