Enable browser plugin compositing by default, but add a flag to disable it.

content/browser/web_contents/web_contents_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/web_contents/web_contents_impl.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
@@ skipping 614 matching lines @@
   prefs.viewport_enabled = command_line.HasSwitch(switches::kEnableViewport);
 
   prefs.deferred_image_decoding_enabled =
       command_line.HasSwitch(switches::kEnableDeferredImageDecoding) ||
       cc::switches::IsImplSidePaintingEnabled();
 
   GetContentClient()->browser()->OverrideWebkitPrefs(rvh, url, &prefs);
 
   // Disable compositing in guests until we have compositing path implemented
   // for guests.
-  bool guest_compositing_enabled = command_line.HasSwitch(
-      switches::kEnableBrowserPluginCompositing);
+  bool guest_compositing_enabled = !command_line.HasSwitch(
+      switches::kDisableBrowserPluginCompositing);
   if (rvh->GetProcess()->IsGuest() && !guest_compositing_enabled) {
     prefs.force_compositing_mode = false;
     prefs.accelerated_compositing_enabled = false;
   }
 
 #if defined(OS_LINUX) && !defined(USE_AURA)
   // Temporary fix for Linux non-Aura capturing. http://crbug.com/174957
   WebContentsImpl* web_contents =
       static_cast<WebContentsImpl*>(WebContents::FromRenderViewHost(rvh));
   if (web_contents && web_contents->capturer_count_ > 0) {
@@ skipping 2854 matching lines @@
 }
 
 BrowserPluginGuestManager*
     WebContentsImpl::GetBrowserPluginGuestManager() const {
   return static_cast<BrowserPluginGuestManager*>(
       GetBrowserContext()->GetUserData(
           browser_plugin::kBrowserPluginGuestManagerKeyName));
 }
 
 }  // namespace content