gpu: Add ARB_occlusion_query support.

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 3b78caf7e89934e64e377dde333d3f5bc5f8b79e..add21a0f08eee9c616737e20950f6f64f27a9df8 100644
--- a/cc/output/gl_renderer.h
+++ b/cc/output/gl_renderer.h
@@ -278,6 +278,7 @@ class CC_EXPORT GLRenderer : public DirectRenderer {
   using OverdrawFeedbackCallback = base::Callback<void(unsigned, int)>;
   void ProcessOverdrawFeedback(std::vector<int>* overdraw,
                                size_t num_expected_results,
+                               int max_result,
                                unsigned query,
                                int multiplier);
 
@@ -364,6 +365,7 @@ class CC_EXPORT GLRenderer : public DirectRenderer {
   BoundGeometry bound_geometry_;
   ColorLUTCache color_lut_cache_;
 
+  bool use_occlusion_query_;
   unsigned offscreen_stencil_renderbuffer_id_ = 0;
   gfx::Size offscreen_stencil_renderbuffer_size_;