[Media, Video] Update WMPI when the pipeline gets a new average keyframe distance.

media/base/pipeline.h

Index: media/base/pipeline.h
diff --git a/media/base/pipeline.h b/media/base/pipeline.h
index b7e2e1a857764f589485bbb4db14c541fd232542..cf3c69ee136abeeec3b51de73087573575b26686 100644
--- a/media/base/pipeline.h
+++ b/media/base/pipeline.h
@@ -62,6 +62,9 @@ class MEDIA_EXPORT Pipeline {
 
     // Executed for the first video frame and whenever opacity changes.
     virtual void OnVideoOpacityChange(bool opaque) = 0;
+
+    // Executed when the average keyframe distance for the video changes.
+    virtual void OnVideoAverageKeyframeDistanceUpdate() = 0;
   };
 
   virtual ~Pipeline() {}