Bug 1288331: [ogg] P2. Fix fast seek mochitest. r=cpearce

Fast seek in the old OggReader is broken: the audio track isn't seeked to the video track in order to preserve A/V sync and we end up always performing an accurate seek which explain why this test succeeded before.
The page index is only made of two entries, and so the first video frame returned after a seek, if within the first index will always have a time of 0.

MozReview-Commit-ID: 2EYzLMWRZAi

--HG--
extra : rebase_source : a7c73a757a841550cc7c5d2a0a7229a037a2bb9f

dom/media/test/manifest.js

@@ -552,7 +552,8 @@ var gFastSeekTests = [
   // Note: the sync points are the points on both the audio and video streams
   // before the keyframes. You can't just assume that the keyframes are the sync
   // points, as the audio required for that sync point may be before the keyframe.
-  { name:"bug516323.indexed.ogv", type:"video/ogg", keyframes:[0, 0.46, 3.06] },
+  // We can only seek at the boundary of a page index. see bug 1289438.
+  { name:"bug516323.indexed.ogv", type:"video/ogg", keyframes:[0, 3.06] },
 ];
 
 function IsWindows8OrLater() {