Bug 1008785 - Ensure the last video frame end time is correct on Android MP4 playback. r=kinetik

content/media/plugins/MediaPluginReader.cpp

@@ -144,9 +144,7 @@ bool MediaPluginReader::DecodeVideoFrame(bool &aKeyframeSkip,
       if (mLastVideoFrame) {
         int64_t durationUs;
         mPlugin->GetDuration(mPlugin, &durationUs);
-        if (durationUs < mLastVideoFrame->mTime) {
-          durationUs = 0;
-        }
+        durationUs = std::max<int64_t>(durationUs - mLastVideoFrame->mTime, 0);
         mVideoQueue.Push(VideoData::ShallowCopyUpdateDuration(mLastVideoFrame,
                                                               durationUs));
         mLastVideoFrame = nullptr;