Avoid GCing an aborting and stopped FileReader.

Avoid GCing an aborting and stopped FileReader.

If a FileReader is abort()ed, a task is scheduled to perform the actual
abort operation. Should the containing Document's ActiveDOMObjects be
stopped before that task gets to run, the FileReader would already
advance to a DONE state and be at risk from being GCed before the abort
task gets to run. If so, it would then access a dead object.

The provided test elicits an assert that shows up the problem, but
doesn't trigger the GC and subsequent access of the dead object.

R=kouhei@chromium.org, tzik@chromium.org
BUG=404513
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180450

[sof, 2014-08-18 09:17:05]

Please take a look.

[kouhei (in TOK), 2014-08-18 10:54:07]

lgtm, but I'm not super confident with this.
tzik: Would you take an another look?

[tzik, 2014-08-18 12:07:35]

lgtm

[sof, 2014-08-18 12:10:37]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2014-08-18 12:11:35]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/sigbjornf@opera.com/478263002/1

[commit-bot: I haz the power, 2014-08-18 12:14:53]

Committed patchset #1 (1) as 180450

[haraken, 2014-08-18 12:27:31]

LGTM