GitLab

Original patch: crrev.com/1020743003.

The GN file is changed so that the tests are no longer depending on the target that was causing link errors on debug GN builds.

TEST=git cl try + mac_chromium_gn_dbg + win8_chromium_gn_dbg

[Media Router] MediaRouter interfaces with stub implementations.

- Updated Media Router data classes.
- Added MediaRouter interface with a stub MediaRouterImpl class.
- MRImpl is a KeyedService and is instantiated via
  its BrowserContextKeyedServiceFactory implementation.
- Added MediaRoutesObserver / MediaSinksObserver interfaces which are
  used by MediaRouter API.

BUG=461815,464199

Review URL: https://codereview.chromium.org/1076973002

Cr-Commit-Position: refs/heads/master@{#324662}