[Cast, Android] Don't hold the wake lock if the video is playing remotely.

Since the video is actually playing on a remote device, there's no need to prevent
the screen from fading and locking.

BUG=420665
TEST=manual

Review URL: https://codereview.chromium.org/644463003

Cr-Commit-Position: refs/heads/master@{#299137}
7 files changed