Adding fading effect for paint rectangles in HUD.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 701 matching lines @@
 
   // If the root render surface has no visible damage, then don't generate a
   // frame at all.
   RenderSurfaceImpl* root_surface =
       active_tree_->root_layer()->render_surface();
   bool root_surface_has_no_visible_damage =
       !root_surface->damage_tracker()->current_damage_rect().Intersects(
           root_surface->content_rect());
   bool root_surface_has_contributing_layers =
       !root_surface->layer_list().empty();
+  bool hud_wants_to_draw_ = active_tree_->hud_layer() &&
+                            active_tree_->hud_layer()->IsAnimatingHUDContents();
   if (root_surface_has_contributing_layers &&
       root_surface_has_no_visible_damage &&
-      active_tree_->LayersWithCopyOutputRequest().empty()) {
+      active_tree_->LayersWithCopyOutputRequest().empty() &&
+      !hud_wants_to_draw_) {
     TRACE_EVENT0("cc",
                  "LayerTreeHostImpl::CalculateRenderPasses::EmptyDamageRect");
     frame->has_no_damage = true;
     DCHECK(!output_surface_->capabilities()
                .draw_and_swap_full_viewport_every_frame);
     return DrawSwapReadbackResult::DRAW_SUCCESS;
   }
 
   TRACE_EVENT1("cc",
                "LayerTreeHostImpl::CalculateRenderPasses",
@@ skipping 2301 matching lines @@
   swap_promise_monitor_.erase(monitor);
 }
 
 void LayerTreeHostImpl::NotifySwapPromiseMonitorsOfSetNeedsRedraw() {
   std::set<SwapPromiseMonitor*>::iterator it = swap_promise_monitor_.begin();
   for (; it != swap_promise_monitor_.end(); it++)
     (*it)->OnSetNeedsRedrawOnImpl();
 }
 
 }  // namespace cc