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

content/browser/renderer_host/render_widget_host_view_gtk.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_gtk.h"
 
 // If this gets included after the gtk headers, then a bunch of compiler
 // errors happen because of a "#define Status int" in Xlib.h, which interacts
 // badly with net::URLRequestStatus::Status.
 #include "content/common/view_messages.h"
@@ skipping 740 matching lines @@
 void RenderWidgetHostViewGtk::Blur() {
   // TODO(estade): We should be clearing native focus as well, but I know of no
   // way to do that without focusing another widget.
   host_->Blur();
 }
 
 bool RenderWidgetHostViewGtk::HasFocus() const {
   return gtk_widget_is_focus(view_.get());
 }
 
+bool RenderWidgetHostViewGtk::IsSurfaceAvailableForCopy() const {
+  return !!host_->GetBackingStore(false);
+}
+
 void RenderWidgetHostViewGtk::Show() {
   gtk_widget_show(view_.get());
 }
 
 void RenderWidgetHostViewGtk::Hide() {
   gtk_widget_hide(view_.get());
 }
 
 bool RenderWidgetHostViewGtk::IsShowing() {
   return gtk_widget_get_visible(view_.get());
@@ skipping 713 matching lines @@
     browser_accessibility_manager_.reset(
         BrowserAccessibilityManager::CreateEmptyDocument(
             parent, static_cast<WebAccessibility::State>(0), this));
   }
   BrowserAccessibilityGtk* root =
       browser_accessibility_manager_->GetRoot()->ToBrowserAccessibilityGtk();
 
   atk_object_set_role(root->GetAtkObject(), ATK_ROLE_HTML_CONTAINER);
   return root->GetAtkObject();
 }