Fix media layout tests that made invalid assumptions about timeupdate.

LayoutTests/media/media-controller-playbackrate.html

Index: LayoutTests/media/media-controller-playbackrate.html
diff --git a/LayoutTests/media/media-controller-playbackrate.html b/LayoutTests/media/media-controller-playbackrate.html
index e5a142b44a91494a8e26532d624c85a48e3cda43..ae5a77ba1cd7a03e299ef288045e0de8cd32ce6e 100644
--- a/LayoutTests/media/media-controller-playbackrate.html
+++ b/LayoutTests/media/media-controller-playbackrate.html
@@ -26,6 +26,12 @@
                 video.defaultPlaybackRate = 0;
                 video.controller.playbackRate = 0;
                 video.controller.defaultPlaybackRate = 0;
+
+                // Wait for bringing up to speed step to complete.

[acolwell GONE FROM CHROMIUM, 2014/09/16 21:46:13]

ditto. 

[scherkus (not reviewing), 2014/09/16 22:13:31]

Done.

+                waitForEventOnce('seeked', seeked);
+            };
+
+            var seeked = function() {
                 waitForEvent('play', play);
                 video.play();
             };