Revert of Revert of Move Event to oilpan's heap

Revert of Revert of Move Event to oilpan's heap (https://codereview.chromium.org/213403004/)

Reason for revert:
Original revert was too aggressive.  Failures are just local to the test, and the original patch fixed bugs.

Original issue's description:
> Revert of Move Event to oilpan's heap (https://codereview.chromium.org/208173004/)
> 
> Reason for revert:
> Seems likely to have caused a number of flaky failures in layout tests in oilpan builds:
> 
> Flakiness dashboard link: http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=http%2Ftests%2Fmedia%2Fmedia-source%2Fwebkitmediasource-closed-on-htmlmediaelement-destruction.html%2Csvg%2Fanimations%2Fsmil-leak-element-instances-noBaseValRef.svg%2Csvg%2Fanimations%2Fsmil-leak-element-instances.svg%2Csvg%2Fanimations%2Fsmil-leak-elements.svg
> 
> Example failure bot: http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20Oilpan/builds/2770
> 
> Example failure:
> --- /mnt/data/b/build/slave/WebKit_Linux_Oilpan/build/layout-test-results/svg/animations/smil-leak-element-instances-noBaseValRef-expected.txt
> +++ /mnt/data/b/build/slave/WebKit_Linux_Oilpan/build/layout-test-results/svg/animations/smil-leak-element-instances-noBaseValRef-actual.txt
> @@ -1 +1 @@
> -PASS
> +FAIL: -3 extra live node(s)
> 
> 
> 
> 
> Original issue's description:
> > Move Event to oilpan's heap
> > 
> > Now there is no test failing when I change RefCounted<Event> to RefCountedGarbageCollected<Event>. Thus this CL does the change.
> > 
> > BUG=340522
> > 
> > Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169941
> 
> TBR=oilpan-reviews@chromium.org,ager@chromium.org,wibling@chromium.org,haraken@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=340522
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170092

TBR=oilpan-reviews@chromium.org,ager@chromium.org,wibling@chromium.org,haraken@chromium.org,sigbjornf@opera.com
NOTREECHECKS=true
NOTRY=true
BUG=340522
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170106

[enne (OOO), 2014-03-26 22:59:31]

Created Revert of Revert of Move Event to oilpan's heap

[commit-bot: I haz the power, 2014-03-26 22:59:40]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/enne@chromium.org/213803002/1

[commit-bot: I haz the power, 2014-03-26 22:59:56]

Change committed as 170106

[haraken, 2014-03-26 23:20:32]

Thanks for gardening! Regarding oilpan bots, it's a responsibility of oilpan
people to make them green. So you don't need to revert CLs that break tests or
even compiles in oilpan bots. I'd be happy if you could just ping
oilpan-reviews@ :)