Remove Media Router impl and BrowserContext factory.

Remove Media Router impl and BrowserContext factory.
The class is now redundant with the Media Router Mojo impl
class (to be landed in an upcoming CL.)

BUG=461815
R=imcheng@chromium.org
TBR=miu@chromium.org

Committed: https://crrev.com/fe41362d4e128777cb7e9a98fb3a87c59d658af2
Cr-Commit-Position: refs/heads/master@{#329659}

[imcheng (use chromium acct), 2015-05-12 22:09:02]

imcheng@google.com changed reviewers:
+ imcheng@google.com

[imcheng (use chromium acct), 2015-05-12 22:09:03]

lgtm

[Kevin M, 2015-05-13 16:50:24]

The CQ bit was checked by kmarshall@chromium.org

[commit-bot: I haz the power, 2015-05-13 16:50:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1137993005/1

[commit-bot: I haz the power, 2015-05-13 16:50:49]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-05-13 16:50:51]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Kevin Marshall, 2015-05-13 16:56:54]

The CQ bit was checked by marshallk@google.com

[commit-bot: I haz the power, 2015-05-13 16:57:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1137993005/1

[Kevin M, 2015-05-13 16:57:33]

kmarshall@chromium.org changed reviewers:
+ miu@chromium.org

[miu, 2015-05-13 16:58:23]

lgtm

[commit-bot: I haz the power, 2015-05-13 17:04:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-13 17:06:14]

Patchset 1 (id:??) landed as
https://crrev.com/fe41362d4e128777cb7e9a98fb3a87c59d658af2
Cr-Commit-Position: refs/heads/master@{#329659}