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 2af2c3091e04adaea2d2c0b298383a841be91659..553f346814c91a746bdbf5efd3cbc3637ca53c03 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 +271,14 @@ 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.
+  void OverdrawFeedback(unsigned query, int category, base::Closure barrier);
+  void UpdateOverdrawCounter() const;
+
   using OverlayResourceLock =
       std::unique_ptr<ResourceProvider::ScopedReadLockGL>;
   using OverlayResourceLockList = std::vector<OverlayResourceLock>;
@@ -543,6 +552,13 @@ class CC_EXPORT GLRenderer : public DirectRenderer {
 
   BoundGeometry bound_geometry_;
   ColorLUTCache color_lut_cache_;
+
+  std::set<int> current_overdraw_;

[danakj, 2017/01/12 00:42:58]

set is very slow, is there a better structure you can use?

[reveman, 2017/01/13 01:27:43]

FYI, this will become a map in a follow up patch where we track the exact amount
of overdraw.

I think set/map is fine. It makes for clean and easy to read code and it's only
used when overdraw tracing is enabled so it doesn't effect normal chrome
performance.

+  unsigned offscreen_stencil_renderbuffer_id_ = 0;
+  gfx::Size offscreen_stencil_renderbuffer_size_;
+  struct PendingOverdrawQuery;
+  std::deque<std::unique_ptr<PendingOverdrawQuery>> pending_overdraw_queries_;

[danakj, 2017/01/12 00:42:58]

deque is very costly for memory
https://bugs.chromium.org/p/chromium/issues/detail?id=674287 is there something
better you can use?

[reveman, 2017/01/13 01:27:43]

Removed this completely from latest version of the patch.

+
   DISALLOW_COPY_AND_ASSIGN(GLRenderer);
 };