Reland of "Expose events in workers as per latest DOM specification"

Reland of "Expose events in workers as per latest DOM specification"

The original CL was reverted (https://codereview.chromium.org/262173006/)
because of some thread safety issues. There has been some work since then
related to thread-safety (e.g. crash if DEFINE_STATIC_LOCAL variables are
misused). So try landing this change again and see if we can determine the cause
of the issues that lead to the earlier revert.

This reverts commit 90cb21f40c8db15868c4e605a0b79fed9b77eb50.

BUG=370011
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=190921

[sadrul, 2015-02-26 02:59:07]

sadrul@chromium.org changed reviewers:
+ kinuko@chromium.org, tkent@chromium.org

[sadrul, 2015-02-26 02:59:08]

Hi! One of the reasons for this patch was reverted earlier was concerns about
the thread-safety of EventDispatchForbiddenScope::isEventDispatchForbidden(). I
have added some ASSERT()s in EventDispatchForbiddenScope to ensure that we do
not actually forbid event-dispatch on non-main thread. I have also added a test
to verify that a custom event created in a worker can be dispatched correctly.
Does this provide sufficient confidence to reland this patch? Or do you think
there are other areas of code that could break from this?

[tkent, 2015-02-26 04:40:46]

lgtm

[kinuko, 2015-02-26 07:36:31]

lgtm

[sadrul, 2015-02-26 14:11:34]

The CQ bit was checked by sadrul@chromium.org

[commit-bot: I haz the power, 2015-02-26 14:12:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/946833004/80001

[commit-bot: I haz the power, 2015-02-26 15:16:18]

Committed patchset #5 (id:80001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=190921