Move content::MediaController to media/base

The MediaController interface and the upcoming MediaStatusObserver do
not have to live in content/public/browser. The media/base folder and
the media namespace is a more generic place for them to live, even if
most of the code that will use them lives in content.

Bug: 820277
Change-Id: I2f91cd88c6f5238723aae8aeff1c323c02f738d4
Reviewed-on: https://chromium-review.googlesource.com/1134090
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Thomas Guilbert <tguilbert@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574690}
18 files changed