This adds the following non-standardized metrics to video receiver stats: - freezeCount - pauseCount - totalFreezesDuration - totalPausesDuration - totalFramesDuration - sumOfSquaredFrameDurations For description of these metrics see https://henbos.github.io/webrtc-provisional-stats/#RTCVideoReceiverStats-dict* Bug: webrtc:10145 Change-Id: I4c76d5651102e73b1592ffed561e6224f2badeb6 Reviewed-on: https://webrtc-review.googlesource.com/c/114840 Reviewed-by: Stefan Holmer <stefan@webrtc.org> Reviewed-by: Henrik Boström <hbos@webrtc.org> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org> Commit-Queue: Sergey Silkin <ssilkin@webrtc.org> Cr-Commit-Position: refs/heads/master@{#26523}