Revert of [Oilpan] Fix wrong usage of HeapCountedSet<EventTarget*>

Revert of [Oilpan] Fix wrong usage of HeapCountedSet<EventTarget*> (patchset #3 id:80001 of https://codereview.chromium.org/1401033002/ )

Reason for revert:
Broke a number of tests on all Oilpan bots,

 http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20Oilpan/builds/29326

Lazy sweeping of EventTargetSet related.

Original issue's description:
> Fix wrong usage of HeapCountedSet<EventTarget*>
>
> BUG=515524
>
> Committed: https://crrev.com/0ab9a39b2347bc686cb6c2a7464acfebe3d4bd10
> Cr-Commit-Position: refs/heads/master@{#353714}

TBR=oilpan-reviews@chromium.org,haraken@chromium.org,peria@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=515524
Committed: https://crrev.com/7261e3643f5e8fde78f93533b2d274f926a8bd8f
Cr-Commit-Position: refs/heads/master@{#353756}

[sof, 2015-10-13 15:21:19]

Created Revert of [Oilpan] Fix wrong usage of HeapCountedSet<EventTarget*>

[commit-bot: I haz the power, 2015-10-13 15:21:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405513003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405513003/1

[commit-bot: I haz the power, 2015-10-13 15:28:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-13 15:29:11]

Patchset 1 (id:??) landed as
https://crrev.com/7261e3643f5e8fde78f93533b2d274f926a8bd8f
Cr-Commit-Position: refs/heads/master@{#353756}

[haraken, 2015-10-13 15:42:18]

Thanks, LGTM

[sof, 2015-10-13 22:27:24]

On 2015/10/13 15:42:18, haraken wrote:
> Thanks, LGTM

it is inconsistent to introduce a transition type here. we don't do that
elsewhere for these manually managed weak refs (cf.
LocalFrame::m_pluginElements).

[haraken, 2015-10-13 23:20:21]

On 2015/10/13 22:27:24, sof wrote:
> On 2015/10/13 15:42:18, haraken wrote:
> > Thanks, LGTM
> 
> it is inconsistent to introduce a transition type here. we don't do that
> elsewhere for these manually managed weak refs (cf.
> LocalFrame::m_pluginElements).

oh, I didn't know that. I'm fine with either way (use a raw pointer or use a
Member) as long as it's consistent through the code base.

[sof, 2015-10-14 06:20:21]

On 2015/10/13 23:20:21, haraken wrote:
> On 2015/10/13 22:27:24, sof wrote:
> > On 2015/10/13 15:42:18, haraken wrote:
> > > Thanks, LGTM
> > 
> > it is inconsistent to introduce a transition type here. we don't do that
> > elsewhere for these manually managed weak refs (cf.
> > LocalFrame::m_pluginElements).
> 
> oh, I didn't know that. I'm fine with either way (use a raw pointer or use a
> Member) as long as it's consistent through the code base.

The on-heap version also needs to trace the backing storage, which wasn't done.
I suggest keeping this type alias as-is. But with a suitable comment etc.

[peria, 2015-10-14 07:13:08]

On 2015/10/14 06:20:21, sof wrote:
> On 2015/10/13 23:20:21, haraken wrote:
> > On 2015/10/13 22:27:24, sof wrote:
> > > On 2015/10/13 15:42:18, haraken wrote:
> > > > Thanks, LGTM
> > > 
> > > it is inconsistent to introduce a transition type here. we don't do that
> > > elsewhere for these manually managed weak refs (cf.
> > > LocalFrame::m_pluginElements).
> > 
> > oh, I didn't know that. I'm fine with either way (use a raw pointer or use a
> > Member) as long as it's consistent through the code base.
> 
> The on-heap version also needs to trace the backing storage, which wasn't
done.
> I suggest keeping this type alias as-is. But with a suitable comment etc.

Thank you for this revert.

I think it good to include this change in
https://codereview.chromium.org/1397073002/
to keep them consistent.
What do you think?