Prevent browser thumbnailer from trying to read from frontbuffer (surface texture) when none exists.

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 "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "base/memory/weak_ptr.h"
@@ skipping 311 matching lines @@
 }
 
 void RenderWidgetHostViewAura::Blur() {
   window_->Blur();
 }
 
 bool RenderWidgetHostViewAura::HasFocus() const {
   return window_->HasFocus();
 }
 
+bool RenderWidgetHostViewAura::IsSurfaceAvailableForCopy() const {
+  return current_surface_ != 0;
+}
+
 void RenderWidgetHostViewAura::Show() {
   window_->Show();
 }
 
 void RenderWidgetHostViewAura::Hide() {
   window_->Hide();
 }
 
 bool RenderWidgetHostViewAura::IsShowing() {
   return window_->IsVisible();
@@ skipping 973 matching lines @@
 RenderWidgetHostView* RenderWidgetHostView::CreateViewForWidget(
     RenderWidgetHost* widget) {
   return new RenderWidgetHostViewAura(widget);
 }
 
 // static
 void content::RenderWidgetHostViewPort::GetDefaultScreenInfo(
     WebKit::WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }