DevTools: fix race conditions while recording film strips

DevTools: fix race conditions while recording film strips

- introduce ResourceTreeModel.{suspendReload,resumeReload} to temporarily
    suspend page reloading;
- use the former to disable page reload for the period we fetch trace in
    the network FilmStripRecorder, as we can't start tracing while
    still retrieving traces;
- disregard DeferredTempFile writes after file was deleted;
- properly indicate frames are being recorded in FilmStripView when reload
    happens during frame recording.

This gets rid of "Tracing is already started" and other errors while repeatedly
reloading a network panel with screenshot recording on.

BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201837

[caseq, 2015-09-04 19:09:11]

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

[caseq, 2015-09-04 21:48:09]

ptal

[dgozman, 2015-09-04 21:53:03]

lgtm

[caseq, 2015-09-04 21:54:06]

The CQ bit was checked by caseq@chromium.org

[commit-bot: I haz the power, 2015-09-04 21:54:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1314783010/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1314783010/20001

[commit-bot: I haz the power, 2015-09-05 01:03:43]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201837