Adding support for VSyncProvider to the software drawing path

cc/output/software_output_device.cc

Index: cc/output/software_output_device.cc
diff --git a/cc/output/software_output_device.cc b/cc/output/software_output_device.cc
index 03f977e7426983a06389db7909d34dfda26a22d3..2c099445b865edfc5604531fb4e39f3d7cf7d113 100644
--- a/cc/output/software_output_device.cc
+++ b/cc/output/software_output_device.cc
@@ -9,6 +9,7 @@
 #include "third_party/skia/include/core/SkBitmapDevice.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "ui/gfx/skia_util.h"
+#include "ui/gl/vsync_provider.h"
 
 namespace cc {
 
@@ -56,4 +57,8 @@ void SoftwareOutputDevice::ReclaimSoftwareFrame(unsigned id) {
   NOTIMPLEMENTED();
 }
 
+gfx::VSyncProvider* SoftwareOutputDevice::GetVSyncProvider() {
+  return vsync_provider_.get();
+}
+
 }  // namespace cc