Allow Preroll() call on VideoRendererImpl without a Flush().

media/filters/video_renderer_impl.h

Index: media/filters/video_renderer_impl.h
diff --git a/media/filters/video_renderer_impl.h b/media/filters/video_renderer_impl.h
index e108e614ee43f4bf2b26433e64af21f377a73913..79c5d824ced66c8565afeab549b7681555cf5da3 100644
--- a/media/filters/video_renderer_impl.h
+++ b/media/filters/video_renderer_impl.h
@@ -129,6 +129,10 @@ class MEDIA_EXPORT VideoRendererImpl
 
   void TransitionToPrerolled_Locked();
 
+  // Returns true of all conditions have been met to transition from
+  // kPrerolling to kPrerolled.
+  bool ShouldTransitionToPrerolled_Locked();
+
   // Runs |statistics_cb_| with |frames_decoded_| and |frames_dropped_|, resets
   // them to 0, and then waits on |frame_available_| for up to the
   // |wait_duration|.