Paint first frame faster, don't crash with no frames during EOS.

media/base/video_frame.h

Index: media/base/video_frame.h
diff --git a/media/base/video_frame.h b/media/base/video_frame.h
index 4ff66ac333dd659f3c9d13523d1b45e1905f8843..c542aed5c69fc914738aba8e83d4e1c35b4937b8 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -420,6 +420,10 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   // Returns a human-readable string describing |*this|.
   std::string AsHumanReadableString();
 
+  // Unique identifier for this video frame; generated at construction time and
+  // guaranteed to be unique within a single process.
+  int unique_id() const { return unique_id_; }
+
  protected:
   friend class base::RefCountedThreadSafe<VideoFrame>;
 
@@ -569,6 +573,9 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
 
   VideoFrameMetadata metadata_;
 
+  // Generated at construction time.
+  const int unique_id_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(VideoFrame);
 };