Perform glReadPixels with PBOs in the gpu, if PBOs are available.

cc/test/test_web_graphics_context_3d.h

Index: cc/test/test_web_graphics_context_3d.h
diff --git a/cc/test/test_web_graphics_context_3d.h b/cc/test/test_web_graphics_context_3d.h
index 4855b0a2de2b9c2bd7d4b1ae8711806d2cab46a5..0652681bc52a9294fb2d22d13007f17e91ed02c9 100644
--- a/cc/test/test_web_graphics_context_3d.h
+++ b/cc/test/test_web_graphics_context_3d.h
@@ -110,6 +110,8 @@ class TestWebGraphicsContext3D : public FakeWebGraphicsContext3D {
   // Takes ownership of the |callback|.
   virtual void signalSyncPoint(unsigned sync_point,
                                WebGraphicsSyncPointCallback* callback);
+  virtual void signalQuery(WebKit::WebGLId query,
+                           WebGraphicsSyncPointCallback* callback);
 
   virtual void setSwapBuffersCompleteCallbackCHROMIUM(
       WebGraphicsSwapBuffersCompleteCallbackCHROMIUM* callback);