Null check MediaSourceRegistry::lookup

Null check MediaSourceRegistry::lookup

A null string cannot be used as a key to a hash stable. Add a null check
and just return null as well.

BUG=620703
Committed: https://crrev.com/ee695fe5fcf12d99bae7a8e6a979610eb8447980
Cr-Commit-Position: refs/heads/master@{#400516}

[boliu, 2016-06-17 17:43:09]

boliu@chromium.org changed reviewers:
+ wolenetz@chromium.org

[boliu, 2016-06-17 17:43:09]

ptal

[wolenetz, 2016-06-17 17:51:56]

The CQ bit was checked by wolenetz@chromium.org

[wolenetz, 2016-06-17 17:51:56]

lgtm

[commit-bot: I haz the power, 2016-06-17 17:52:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2075183002/1

[commit-bot: I haz the power, 2016-06-17 21:50:30]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-06-17 21:52:55]

Description was changed from

==========
Null check MediaSourceRegistry::lookup

A null string cannot be used as a key to a hash stable. Add a null check
and just return null as well.

BUG=620703
==========

to

==========
Null check MediaSourceRegistry::lookup

A null string cannot be used as a key to a hash stable. Add a null check
and just return null as well.

BUG=620703

Committed: https://crrev.com/ee695fe5fcf12d99bae7a8e6a979610eb8447980
Cr-Commit-Position: refs/heads/master@{#400516}
==========

[commit-bot: I haz the power, 2016-06-17 21:52:56]

Patchset 1 (id:??) landed as
https://crrev.com/ee695fe5fcf12d99bae7a8e6a979610eb8447980
Cr-Commit-Position: refs/heads/master@{#400516}