[DevTools] Fix crash in InspectorTracingAgent.

[DevTools] Fix crash in InspectorTracingAgent.

|m_state| can be null at the time we call setLayerTreeId.

BUG=591622
Committed: https://crrev.com/b6eceb74841afe66e73115c84317b3bbe29b124f
Cr-Commit-Position: refs/heads/master@{#379174}

[dgozman, 2016-03-03 20:48:39]

dgozman@chromium.org changed reviewers:
+ caseq@chromium.org

[dgozman, 2016-03-03 20:48:40]

Take a look please.

[caseq, 2016-03-04 00:38:51]

The CQ bit was checked by caseq@chromium.org

[caseq, 2016-03-04 00:38:52]

lgtm

[commit-bot: I haz the power, 2016-03-04 00:39:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1761793004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1761793004/1

[commit-bot: I haz the power, 2016-03-04 01:53:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-04 01:54:45]

Description was changed from

==========
[DevTools] Fix crash in InspectorTracingAgent.

|m_state| can be null at the time we call setLayerTreeId.

BUG=591622
==========

to

==========
[DevTools] Fix crash in InspectorTracingAgent.

|m_state| can be null at the time we call setLayerTreeId.

BUG=591622

Committed: https://crrev.com/b6eceb74841afe66e73115c84317b3bbe29b124f
Cr-Commit-Position: refs/heads/master@{#379174}
==========

[commit-bot: I haz the power, 2016-03-04 01:54:46]

Patchset 1 (id:??) landed as
https://crrev.com/b6eceb74841afe66e73115c84317b3bbe29b124f
Cr-Commit-Position: refs/heads/master@{#379174}