[Chromecast] Add service for "displaying" cast web contents.
Audio-only Android builds should not start an activity, so this change
adds the option of using a service.
Rather than directly starting an activity to display cast apps,
CastContentWindowAndroid uses CastWebContentsComponent to start and
interact with whichever kind of component is appropriate for the build.
This is controlled with the build flag 'display_web_contents_in_service', which
defaults to is_cast_audio_only.
BUG=internal 36596922
Review-Url: https://codereview.chromium.org/2874943002
Cr-Commit-Position: refs/heads/master@{#473670}
9 files changed