Make RenderWidgetHostViewAura::CopyFromCompositingSurface readback layer

content/browser/renderer_host/render_widget_host_view_base.cc

Index: content/browser/renderer_host/render_widget_host_view_base.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_base.cc b/content/browser/renderer_host/render_widget_host_view_base.cc
index 1b02a90f0221c66a1a7fb8f739e500f64c128ee5..4d556002bd7eff99cfda2f2227ae68a5481fc355 100644
--- a/content/browser/renderer_host/render_widget_host_view_base.cc
+++ b/content/browser/renderer_host/render_widget_host_view_base.cc
@@ -356,7 +356,8 @@ RenderWidgetHostViewBase::RenderWidgetHostViewBase()
       showing_context_menu_(false),
       selection_text_offset_(0),
       selection_range_(ui::Range::InvalidRange()),
-      current_device_scale_factor_(0) {
+      current_device_scale_factor_(0),
+      renderer_frame_number_(0) {
 }
 
 RenderWidgetHostViewBase::~RenderWidgetHostViewBase() {
@@ -521,4 +522,12 @@ void RenderWidgetHostViewBase::OnOverscrolled(
     gfx::Vector2dF current_fling_velocity) {
 }
 
+uint32 RenderWidgetHostViewBase::RendererFrameNumber() {
+  return renderer_frame_number_;
+}
+
+void RenderWidgetHostViewBase::DidReceiveRendererFrame() {
+  ++renderer_frame_number_;
+}
+
 }  // namespace content