Add chromium side flag for enabling/disabling layer squashing.

content/browser/renderer_host/render_view_host_impl.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 "content/browser/renderer_host/render_view_host_impl.h"
 
 #include <set>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 356 matching lines @@
       !command_line.HasSwitch(switches::kDisableSiteSpecificQuirks);
   prefs.allow_file_access_from_file_urls =
       command_line.HasSwitch(switches::kAllowFileAccessFromFiles);
 
   prefs.accelerated_compositing_for_overflow_scroll_enabled = false;
   if (command_line.HasSwitch(switches::kEnableAcceleratedOverflowScroll))
     prefs.accelerated_compositing_for_overflow_scroll_enabled = true;
   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;
   if (command_line.HasSwitch(switches::kDisableAcceleratedScrollableFrames))
     prefs.accelerated_compositing_for_scrollable_frames_enabled = false;
 
   prefs.composited_scrolling_for_frames_enabled = false;
   if (command_line.HasSwitch(switches::kEnableCompositedScrollingForFrames))
     prefs.composited_scrolling_for_frames_enabled = true;
   if (command_line.HasSwitch(switches::kDisableCompositedScrollingForFrames))
@@ skipping 32 matching lines @@
   prefs.accelerated_compositing_for_plugins_enabled =
       !command_line.HasSwitch(switches::kDisableAcceleratedPlugins);
   prefs.accelerated_compositing_for_video_enabled =
       !command_line.HasSwitch(switches::kDisableAcceleratedVideo);
   prefs.fullscreen_enabled =
       !command_line.HasSwitch(switches::kDisableFullScreen);
   prefs.lazy_layout_enabled =
       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 =
       command_line.HasSwitch(switches::kEnableExperimentalWebSocket);
   if (command_line.HasSwitch(cc::switches::kEnablePinchVirtualViewport)) {
     prefs.pinch_virtual_viewport_enabled = true;
     prefs.pinch_overlay_scrollbar_thickness = 10;
   }
   prefs.use_solid_color_scrollbars = command_line.HasSwitch(
       switches::kEnableOverlayScrollbars);
@@ skipping 1839 matching lines @@
 void RenderViewHostImpl::AttachToFrameTree() {
   FrameTree* frame_tree = delegate_->GetFrameTree();
 
   frame_tree->SwapMainFrame(main_render_frame_host_.get());
   if (main_frame_id() != FrameTreeNode::kInvalidFrameId) {
     frame_tree->OnFirstNavigationAfterSwap(main_frame_id());
   }
 }
 
 }  // namespace content