Enable underlay strategy by default in OverlayProcessor

cc/output/overlay_processor.cc

 // Copyright 2014 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/output/overlay_processor.h"
 
 #include "cc/output/output_surface.h"
 #include "cc/output/overlay_strategy_single_on_top.h"
+#include "cc/output/overlay_strategy_underlay.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 #include "ui/gfx/transform.h"
 
 namespace cc {
 
 OverlayProcessor::OverlayProcessor(OutputSurface* surface,
                                    ResourceProvider* resource_provider)
     : surface_(surface), resource_provider_(resource_provider) {}
 
 void OverlayProcessor::Initialize() {
   DCHECK(surface_);
   if (!resource_provider_)
     return;
 
   OverlayCandidateValidator* candidates =
       surface_->GetOverlayCandidateValidator();
   if (candidates) {
     strategies_.push_back(scoped_ptr<Strategy>(
         new OverlayStrategySingleOnTop(candidates, resource_provider_)));
+    strategies_.push_back(scoped_ptr<Strategy>(
+        new OverlayStrategyUnderlay(candidates, resource_provider_)));
   }
 }
 
 OverlayProcessor::~OverlayProcessor() {}
 
 void OverlayProcessor::ProcessForOverlays(
     RenderPassList* render_passes_in_draw_order,
     OverlayCandidateList* candidate_list) {
   for (StrategyList::iterator it = strategies_.begin(); it != strategies_.end();
        ++it) {
     if ((*it)->Attempt(render_passes_in_draw_order, candidate_list))
       return;
   }
 }
 
 }  // namespace cc