cc: Implement overdraw feedback debugging feature.

cc/output/gl_renderer.h

Index: cc/output/gl_renderer.h
diff --git a/cc/output/gl_renderer.h b/cc/output/gl_renderer.h
index c701318855ad04b5ea9db941a7ea0f1d97fdcb99..3b78caf7e89934e64e377dde333d3f5bc5f8b79e 100644
--- a/cc/output/gl_renderer.h
+++ b/cc/output/gl_renderer.h
@@ -270,6 +270,17 @@ class CC_EXPORT GLRenderer : public DirectRenderer {
   void ScheduleRenderPassDrawQuad(const CALayerOverlay* ca_layer_overlay,
                                   DrawingFrame* external_frame);
 
+  // Setup/flush all pending overdraw feedback to framebuffer.
+  void SetupOverdrawFeedback();
+  void FlushOverdrawFeedback(const DrawingFrame* frame,
+                             const gfx::Rect& output_rect);
+  // Process overdraw feedback from query.
+  using OverdrawFeedbackCallback = base::Callback<void(unsigned, int)>;
+  void ProcessOverdrawFeedback(std::vector<int>* overdraw,
+                               size_t num_expected_results,
+                               unsigned query,
+                               int multiplier);
+
   using OverlayResourceLock =
       std::unique_ptr<ResourceProvider::ScopedReadLockGL>;
   using OverlayResourceLockList = std::vector<OverlayResourceLock>;
@@ -353,6 +364,9 @@ class CC_EXPORT GLRenderer : public DirectRenderer {
   BoundGeometry bound_geometry_;
   ColorLUTCache color_lut_cache_;
 
+  unsigned offscreen_stencil_renderbuffer_id_ = 0;
+  gfx::Size offscreen_stencil_renderbuffer_size_;
+
   base::WeakPtrFactory<GLRenderer> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(GLRenderer);