Timeline: fix expansion arrow appearing on rows with no visible children

Timeline: fix expansion arrow appearing on rows with no visible children

We used to check TimelinePresentationRecord.expandable(), but it was accidrently replaced
with hasPresentationChildren(), which is not the same now, since we keep hidden records
in the presentation model.

R=pfeldman@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169620

[pfeldman, 2014-03-19 16:35:09]

lgtm

[caseq, 2014-03-19 18:03:17]

The CQ bit was checked by caseq@chromium.org

[commit-bot: I haz the power, 2014-03-19 18:03:36]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/caseq@chromium.org/201823003/1

[commit-bot: I haz the power, 2014-03-19 18:06:19]

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

[commit-bot: I haz the power, 2014-03-19 18:06:19]

Try jobs failed on following builders:
  tryserver.blink on win_blink_rel

[caseq, 2014-03-20 05:45:12]

Committed patchset #1 manually as r169620 (presubmit successful).