Read compositor VSync information from platform, when possible

content/browser/compositor/gpu_browser_compositor_output_surface.h

Index: content/browser/compositor/gpu_browser_compositor_output_surface.h
diff --git a/content/browser/compositor/gpu_browser_compositor_output_surface.h b/content/browser/compositor/gpu_browser_compositor_output_surface.h
index c67783939c6db43b6e54ab30a7beb6d001f43ae7..ab883b3583193bb5995da805507207c513442ca8 100644
--- a/content/browser/compositor/gpu_browser_compositor_output_surface.h
+++ b/content/browser/compositor/gpu_browser_compositor_output_surface.h
@@ -7,6 +7,10 @@
 
 #include "content/browser/compositor/browser_compositor_output_surface.h"
 
+namespace ui {
+class Compositor;
+}
+
 namespace content {
 
 // Adapts a WebGraphicsContext3DCommandBufferImpl into a
@@ -19,8 +23,7 @@ class GpuBrowserCompositorOutputSurface
       const scoped_refptr<ContextProviderCommandBuffer>& context,
       int surface_id,
       IDMap<BrowserCompositorOutputSurface>* output_surface_map,
-      base::MessageLoopProxy* compositor_message_loop,
-      base::WeakPtr<ui::Compositor> compositor);
+      ui::Compositor* compositor);
 
   virtual ~GpuBrowserCompositorOutputSurface();