Allow to have a transparent UA dependent background.

content/browser/renderer_host/render_widget_host_view_aura.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_widget_host_view_aura.h"
 
 #include <set>
 #include <utility>
 
 #include "base/auto_reset.h"
@@ skipping 791 matching lines @@
   HandleParentBoundsChanged();
 }
 
 void RenderWidgetHostViewAura::Focus() {
   // Make sure we have a FocusClient before attempting to Focus(). In some
   // situations we may not yet be in a valid Window hierarchy (such as reloading
   // after out of memory discarded the tab).
   aura::client::FocusClient* client = aura::client::GetFocusClient(window_);
   if (client)
     window_->Focus();
+
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kTransparentBackgroundRWHV)) {
+    SetBackgroundColor(SK_ColorTRANSPARENT);
+  }
 }
 
 bool RenderWidgetHostViewAura::HasFocus() const {
   return window_->HasFocus();
 }
 
 bool RenderWidgetHostViewAura::IsSurfaceAvailableForCopy() const {
   return delegated_frame_host_->CanCopyToBitmap();
 }
 
@@ skipping 2119 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // RenderWidgetHostViewBase, public:
 
 // static
 void RenderWidgetHostViewBase::GetDefaultScreenInfo(WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }
 
 }  // namespace content