Adding support for VSyncProvider to the software drawing path

cc/output/software_output_device.h

Index: cc/output/software_output_device.h
diff --git a/cc/output/software_output_device.h b/cc/output/software_output_device.h
index 9e2de88b04869416b57413717644f6c611c43fd1..1d5ec847faf449ac63a38a3625f48a9a4bfc4ccf 100644
--- a/cc/output/software_output_device.h
+++ b/cc/output/software_output_device.h
@@ -17,6 +17,10 @@
 class SkBitmap;
 class SkCanvas;
 
+namespace gfx {
+class VSyncProvider;
+}
+
 namespace cc {
 
 class SoftwareFrameData;
@@ -65,6 +69,10 @@ class CC_EXPORT SoftwareOutputDevice {
   // displayed.
   virtual void ReclaimSoftwareFrame(unsigned id);
 
+  // VSyncProvider used to update the timer used to schedule draws with the
+  // hardware vsync. Return NULL if a provider doesn't exist.
+  virtual gfx::VSyncProvider* GetVSyncProvider();
+
  protected:
   gfx::Size viewport_size_;
   gfx::Rect damage_rect_;