Avoid sending empty OnRepaint msgs and propagate window damage correctly

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index fc2caddca62d0efa77e13539c7ec29cef241e7cb..47587c04c7522f41d073e27bdb170fd3d707fd7f 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -334,6 +334,10 @@ void RenderWidgetCompositor::SetOverdrawBottomHeight(
   layer_tree_host_->SetOverdrawBottomHeight(overdraw_bottom_height);
 }
 
+void RenderWidgetCompositor::SetNeedsRedrawRect(gfx::Rect damage_rect) {
+  layer_tree_host_->SetNeedsRedrawRect(damage_rect);
+}
+
 bool RenderWidgetCompositor::initialize(cc::LayerTreeSettings settings) {
   scoped_ptr<cc::Thread> impl_thread;
   scoped_refptr<base::MessageLoopProxy> compositor_message_loop_proxy =