Bug 1159171: [MSE] P4. Changing waiting time value. r=edwin.

When ffmpeg is enabled, it will use the FFmpeg's VPX decoder. FFmpeg appears to always buffer 15 frames before returning one (this is the same with h264) causing the waiting event to be fired much earlier than when using libvpx

dom/media/mediasource/test/test_BufferingWait.html

@@ -41,14 +41,14 @@ runWithMSE(function(ms, v) {
       /* Note - Missing |46712, 67833 - 46712| segment here corresponding to (0.8, 1.2] */
       /* Note - Missing |67833, 88966 - 67833| segment here corresponding to (1.2, 1.6]  */
       loadSegment.bind(null, sb, new Uint8Array(arrayBuffer, 88966))).then(function() {
-        var promise = waitUntilTime(0.7);
+        var promise = waitUntilTime(0.27);
         info("Playing video. It should play for a bit, then fire 'waiting'");
         v.play();
         return promise;
       }).then(function() {
         window.firstStop = Date.now();
         loadSegment(sb, new Uint8Array(arrayBuffer, 46712, 67833 - 46712));
-        return waitUntilTime(1.0);
+        return waitUntilTime(0.66);
       }).then(function() {
         var waitDuration = (Date.now() - window.firstStop) / 1000;
         ok(waitDuration < 15, "Should not spend an inordinate amount of time buffering: " + waitDuration);