Display skips swapping if overlays draw the damage

cc/output/renderer.h

 // Copyright 2012 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_RENDERER_H_
 #define CC_OUTPUT_RENDERER_H_
 
 #include "base/basictypes.h"
 #include "cc/base/cc_export.h"
 #include "cc/output/renderer_capabilities.h"
 #include "cc/output/renderer_settings.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace cc {
 
 class CompositorFrameAck;
 class CompositorFrameMetadata;
 class RenderPass;
 class RenderPassId;
 class ScopedResource;
 class Task;
 
 typedef std::vector<scoped_ptr<RenderPass>> RenderPassList;
 
+enum class DrawFrameResult {
+  DID_DRAW,
+  // No drawing was done because overlay planes accounted for the damage.
+  DAMAGE_DRAWN_BY_OVERLAYS,
+};
+
 struct RendererCapabilitiesImpl {
   RendererCapabilitiesImpl();
   ~RendererCapabilitiesImpl();
 
   // Capabilities copied to main thread.
   ResourceFormat best_texture_format;
   bool allow_partial_texture_updates;
   int max_texture_size;
   bool using_shared_memory_resources;
 
@@ skipping 21 matching lines @@
 
   virtual void DecideRenderPassAllocationsForFrame(
       const RenderPassList& render_passes_in_draw_order) {}
   virtual bool HasAllocatedResourcesForTesting(RenderPassId id) const;
 
   // This passes ownership of the render passes to the renderer. It should
   // consume them, and empty the list. The parameters here may change from frame
   // to frame and should not be cached.
   // The |device_viewport_rect| and |device_clip_rect| are in non-y-flipped
   // window space.
-  virtual void DrawFrame(RenderPassList* render_passes_in_draw_order,
-                         float device_scale_factor,
-                         const gfx::Rect& device_viewport_rect,
-                         const gfx::Rect& device_clip_rect,
-                         bool disable_picture_quad_image_filtering) = 0;
+  virtual DrawFrameResult DrawFrame(
+      RenderPassList* render_passes_in_draw_order,
+      float device_scale_factor,
+      const gfx::Rect& device_viewport_rect,
+      const gfx::Rect& device_clip_rect,
+      bool disable_picture_quad_image_filtering) = 0;
 
   // Waits for rendering to finish.
   virtual void Finish() = 0;
 
   // Puts backbuffer onscreen.
   virtual void SwapBuffers(const CompositorFrameMetadata& metadata) = 0;
   virtual void ReceiveSwapBuffersAck(const CompositorFrameAck& ack) {}
 
   bool visible() const { return visible_; }
   void SetVisible(bool visible);
 
  protected:
   Renderer(RendererClient* client, const RendererSettings* settings)
       : client_(client), settings_(settings), visible_(true) {}
 
   virtual void DidChangeVisibility() = 0;
 
   RendererClient* client_;
   const RendererSettings* settings_;
   bool visible_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Renderer);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_RENDERER_H_