DevTools: do not show gray time for unaccounted time on threads other than main

DevTools: do not show gray time for unaccounted time on threads other than main

This reverts to old behavior of not including "other" time (i.e. time
unaccounted by specific timeline events) from threads other than main
into Frame statistics. This was a collateral damage from r196216, as
we started to gather top-level tasks from all frames. While it might not technically be a bug, it currently produces lots of gray in Frames and looks rather confusing.

BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196498

[caseq, 2015-06-04 10:18:28]

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

[caseq, 2015-06-04 10:18:40]

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

[yurys, 2015-06-04 11:07:15]

lgtm

[caseq, 2015-06-04 11:12:07]

The CQ bit was checked by caseq@chromium.org

[commit-bot: I haz the power, 2015-06-04 11:12:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1167893002/1

[commit-bot: I haz the power, 2015-06-04 13:13:06]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196498