Timeline: fix NPE in heavy stack view when clearing Timeline

Timeline: fix NPE in heavy stack view when clearing Timeline

BUG=698119
Review-Url: https://codereview.chromium.org/2727233004
Cr-Commit-Position: refs/heads/master@{#454511}
Committed: https://chromium.googlesource.com/chromium/src/+/c8c1429588c2190eb5562d57c0e0ba3b4cbe6f8d

[caseq, 2017-03-03 02:47:31]

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

[alph, 2017-03-03 02:57:05]

The CQ bit was checked by alph@chromium.org

[alph, 2017-03-03 02:57:06]

lgtm

[commit-bot: I haz the power, 2017-03-03 02:57:36]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-03-03 04:29:51]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1488509825651150, "parent_rev":
"519542818dce5ee91f37f3c87b0014a974618f13", "commit_rev":
"c8c1429588c2190eb5562d57c0e0ba3b4cbe6f8d"}

[commit-bot: I haz the power, 2017-03-03 04:30:56]

Description was changed from

==========
Timeline: fix NPE in heavy stack view when clearing Timeline

BUG=698119
==========

to

==========
Timeline: fix NPE in heavy stack view when clearing Timeline

BUG=698119

Review-Url: https://codereview.chromium.org/2727233004
Cr-Commit-Position: refs/heads/master@{#454511}
Committed:
https://chromium.googlesource.com/chromium/src/+/c8c1429588c2190eb5562d57c0e0...
==========

[commit-bot: I haz the power, 2017-03-03 04:30:57]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/c8c1429588c2190eb5562d57c0e0...