Add underlays and split off common overlay functionality

cc/output/overlay_strategy_underlay.h

+// 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.
+
+#ifndef CC_OUTPUT_OVERLAY_STRATEGY_UNDERLAY_H_
+#define CC_OUTPUT_OVERLAY_STRATEGY_UNDERLAY_H_
+
+#include "cc/output/overlay_strategy_common.h"
+
+namespace cc {
+class StreamVideoDrawQuad;
+class TextureDrawQuad;
+
+// The underlay strategy looks for a video quad without regard to quads above
+// it. The video is "underlaid" through a black transparent quad substituted
+// for the video quad. The overlay content can then be blended in by the
+// hardware under the the scene. This is only valid for overlay contents that
+// are fully opaque.
+class CC_EXPORT OverlayStrategyUnderlay : public OverlayStrategyCommon {
+ public:
+  OverlayStrategyUnderlay(OverlayCandidateValidator* capability_checker,
+                          ResourceProvider* resource_provider);
+  bool Attempt(RenderPassList* render_passes_in_draw_order,
+               OverlayCandidateList* candidate_list) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(OverlayStrategyUnderlay);
+};
+
+}  // namespace cc
+
+#endif  // CC_OUTPUT_OVERLAY_STRATEGY_UNDERLAY_H_