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 1891 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