Mac Overlays: Allow multiple overlays with sandwich strategy

cc/output/overlay_strategy_underlay.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_strategy_underlay.h"
 
 #include "cc/output/overlay_candidate_validator.h"
 #include "cc/quads/draw_quad.h"
 #include "cc/quads/solid_color_draw_quad.h"
 
 namespace cc {
 
 OverlayStrategyUnderlay::~OverlayStrategyUnderlay() {}
 
-bool OverlayStrategyUnderlay::TryOverlay(
+QuadList::Iterator OverlayStrategyUnderlay::TryOverlay(
     OverlayCandidateValidator* capability_checker,
     RenderPassList* render_passes_in_draw_order,
     OverlayCandidateList* candidate_list,
     const OverlayCandidate& candidate,
     QuadList::Iterator candidate_iterator,
     float device_scale_factor) {
   RenderPass* root_render_pass = render_passes_in_draw_order->back();
   QuadList& quad_list = root_render_pass->quad_list;
 
   // Add our primary surface.
@@ skipping 13 matching lines @@
   // need to switch out the video quad with a black transparent one.
   if (candidates[1].overlay_handled) {
     const SharedQuadState* shared_quad_state =
         candidate_iterator->shared_quad_state;
     gfx::Rect rect = candidate_iterator->visible_rect;
     SolidColorDrawQuad* replacement =
         quad_list.ReplaceExistingElement<SolidColorDrawQuad>(
             candidate_iterator);
     replacement->SetAll(shared_quad_state, rect, rect, rect, false,
                         SK_ColorTRANSPARENT, true);
+    DCHECK(candidate_list->empty());
     candidate_list->swap(candidates);

[ccameron, 2015/09/02 22:22:33]

same issue about return values here.

-    return true;
   }
-  return false;
+
+  return quad_list.end();
 }
 
 }  // namespace cc