Correct condition and flag state for skipping PLAY request.
* When PLAY request for casted video is skipped, this.playInProgress_ was not cleared and this inconsistent state prevented the video from being played. I cleared the flag in this case.
* When PAUSE reqeust is in progress, incoming PLAY request should not be skipped. So I added a condition to skip the PLAY request.
BUG=417520,417538
TEST=manually tested the steps described in both bugs.
Review URL: https://codereview.chromium.org/
603413003
Cr-Commit-Position: refs/heads/master@{#297137}