Mac Overlays: Add sandwich strategy

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) : surface_(surface) {
 }
 
 void OverlayProcessor::Initialize() {
   DCHECK(surface_);
-
-  OverlayCandidateValidator* candidates =
+  OverlayCandidateValidator* validator =
       surface_->GetOverlayCandidateValidator();
-  if (candidates) {
-    strategies_.push_back(
-        scoped_ptr<Strategy>(new OverlayStrategySingleOnTop(candidates)));
-    strategies_.push_back(
-        scoped_ptr<Strategy>(new OverlayStrategyUnderlay(candidates)));
-  }
+  if (validator)
+    validator->GetStrategies(&strategies_);
 }
 
 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))
+    if ((*it)->Attempt(render_passes_in_draw_order, candidate_list,
+                       surface_->device_scale_factor())) {
       return;
+    }
   }
 }
 
 }  // namespace cc