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..2ccaa721efe81f614704250eb67addd3f5e54c6f 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 CLOCK_MONOTONIC time (in microseconds) for the most recent screen

[piman, 2012/10/24 16:56:54]

CLOCK_MONOTONIC is a linux-only concept. Maybe the best here is to pass
base::TimeTicks which is a platform independent representation.

At the same time, exposing "media stream counter" and "swap buffer counter"
isn't meaningful in the cross-platform interface if it's not available and not
used anywhere.
We should make this expose the last tick time and the tick rate (or interval),
because that's exactly what we need, and what we may be able to provide on all
platforms.

[ajuma, 2012/10/26 20:12:39]

Done.

+  // refresh, along with the values of the Media Stream Counter (which counts
+  // screen refreshes) and the Swap Buffer Counter. Returns false on error,
+  // including when these values are unavailable.
+  virtual bool GetSyncValues(int64* monotonicTime,

[piman, 2012/10/24 16:56:54]

nit: chrome style for parameters

[ajuma, 2012/10/26 20:12:39]

Done.

+                             int64* mediaStreamCounter,
+                             int64* 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* monotonicTime,
+                             int64* mediaStreamCounter,
+                             int64* swapBufferCounter) OVERRIDE;
 
   GLSurface* surface() const { return surface_.get(); }