[Chromecast] Fix issue where new playback rate was never used

In some cases where the old playback rate was 1.0 and was in passthrough
mode, the new playback rate would never start being used. This uses a
more correct check to determine if the old rate is complete.

BUG= internal b/27450476

Review-Url: https://codereview.chromium.org/2683993004
Cr-Commit-Position: refs/heads/master@{#449209}
1 file changed