[Media Router] Do not issue a tab mirroring sinks query if tab is not valid.

[Media Router] Do not issue a tab mirroring sinks query if tab is not valid.

It is possible to bring up the MR UI outside the context of a valid tab.
In those cases we should omit TAB_MIRROR is one of the cast modes and
not start a sinks query for the tab mirror MediaSource.

BUG=591855
Committed: https://crrev.com/236fddad6b5bcd9d00ead4c19d18e6fbd459d143
Cr-Commit-Position: refs/heads/master@{#379872}

[imcheng, 2016-03-04 18:56:52]

imcheng@chromium.org changed reviewers:
+ apacible@chromium.org

[imcheng, 2016-03-04 18:56:53]

PTAL

[apacible, 2016-03-07 18:01:42]

lgtm

[imcheng, 2016-03-08 18:03:38]

The CQ bit was checked by imcheng@chromium.org

[commit-bot: I haz the power, 2016-03-08 18:03:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1761793005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1761793005/20001

[commit-bot: I haz the power, 2016-03-08 18:50:50]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-03-08 18:52:37]

Description was changed from

==========
[Media Router] Do not issue a tab mirroring sinks query if tab is not valid.

It is possible to bring up the MR UI outside the context of a valid tab.
In those cases we should omit TAB_MIRROR is one of the cast modes and
not start a sinks query for the tab mirror MediaSource.

BUG=591855
==========

to

==========
[Media Router] Do not issue a tab mirroring sinks query if tab is not valid.

It is possible to bring up the MR UI outside the context of a valid tab.
In those cases we should omit TAB_MIRROR is one of the cast modes and
not start a sinks query for the tab mirror MediaSource.

BUG=591855

Committed: https://crrev.com/236fddad6b5bcd9d00ead4c19d18e6fbd459d143
Cr-Commit-Position: refs/heads/master@{#379872}
==========

[commit-bot: I haz the power, 2016-03-08 18:52:38]

Patchset 2 (id:??) landed as
https://crrev.com/236fddad6b5bcd9d00ead4c19d18e6fbd459d143
Cr-Commit-Position: refs/heads/master@{#379872}