Add underlays and split off common overlay functionality

cc/output/overlay_strategy_underlay.h

Index: cc/output/overlay_strategy_underlay.h
diff --git a/cc/output/overlay_strategy_underlay.h b/cc/output/overlay_strategy_underlay.h
new file mode 100644
index 0000000000000000000000000000000000000000..7b11e7e0a42ce2741b24c9c0548af4ee8e93bf35
--- /dev/null
+++ b/cc/output/overlay_strategy_underlay.h
@@ -0,0 +1,37 @@
+// 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 "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/cc_export.h"
+#include "cc/output/overlay_candidate.h"
+#include "cc/output/overlay_processor.h"

[alexst (slow to review), 2015/03/18 21:37:58]

Do you need this include in the header?

[achaulk, 2015/03/23 19:16:03]

Nope, removed

+#include "cc/output/overlay_strategy_common.h"
+#include "cc/quads/render_pass.h"
+
+namespace cc {
+class StreamVideoDrawQuad;
+class TextureDrawQuad;
+
+// The underlay strategy looks for a video quad without regard to quads above

[danakj, 2015/03/18 21:30:14]

Can you mention this is only valid for a quad that is drawn opaquely so that the
hole punching does not modify the visual result?

[achaulk, 2015/03/23 19:16:03]

Done.

+// it. The video is "underlaid" through a black transparent quad substituted
+// for the video quad. Video can then be blended in by the hardware on top of

[alexst (slow to review), 2015/03/18 21:37:58]

..blended in by the hardware below the scene?

Since it's an underlay

[achaulk, 2015/03/23 19:16:03]

Sure

+// the scene.
+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_