Send vsync timebase updates to the browser compositor

ui/gl/gl_surface.h

Index: ui/gl/gl_surface.h
diff --git a/ui/gl/gl_surface.h b/ui/gl/gl_surface.h
index 4ecc47223a38f9f642cd81e0aea2ab74614e029f..83a841e18310d5934d54613e13aa1a161c0f5d75 100644
--- a/ui/gl/gl_surface.h
+++ b/ui/gl/gl_surface.h
@@ -102,6 +102,14 @@ class GL_EXPORT GLSurface : public base::RefCounted<GLSurface> {
   // Get the GL pixel format of the surface, if available.
   virtual unsigned GetFormat();
 
+  // Get the Unadjusted System Time for the most recent screen refresh, along
+  // with the values of the Media Stream Counter (which counts refreshes) and
+  // the Swap Buffer Counter. Returns false on error, including when these
+  // values are unavailable.
+  virtual bool GetSyncValues(int64_t* systemTime,
+                             int64_t* mediaStreamCounter,
+                             int64_t* swapBufferCounter);
+
   // Create a GL surface that renders directly to a view.
   static scoped_refptr<GLSurface> CreateViewGLSurface(
       bool software,
@@ -153,6 +161,9 @@ class GL_EXPORT GLSurfaceAdapter : public GLSurface {
   virtual void* GetDisplay() OVERRIDE;
   virtual void* GetConfig() OVERRIDE;
   virtual unsigned GetFormat() OVERRIDE;
+  virtual bool GetSyncValues(int64_t* systemTime,
+                             int64_t* mediaStreamCounter,
+                             int64_t* swapBufferCounter) OVERRIDE;
 
   GLSurface* surface() const { return surface_.get(); }