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 65918a8e68e399795f3911e315011db923f56ef0..ae1b4b550b3d02e714952b522da68a2422d3989e 100644
--- a/cc/output/gl_renderer.h
+++ b/cc/output/gl_renderer.h
@@ -6,6 +6,7 @@
 #define CC_OUTPUT_GL_RENDERER_H_
 
 #include <deque>
+#include <set>
 #include <vector>
 
 #include "base/cancelable_callback.h"
@@ -270,6 +271,18 @@ 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 OverdrawResult = std::set<int>;
+  void ProcessOverdrawFeedback(unsigned query,
+                               int category,
+                               OverdrawResult* overdraw,
+                               const base::Closure& callback);
+  static void UpdateOverdrawCounter(const OverdrawResult* overdraw);
+
   using OverlayResourceLock =
       std::unique_ptr<ResourceProvider::ScopedReadLockGL>;
   using OverlayResourceLockList = std::vector<OverlayResourceLock>;
@@ -363,6 +376,9 @@ 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);