Oilpan: Change adoptRef() in the Event hierarchy to adoptRefWillBeRefCountedGarbageCollected()
Oilpan: Change adoptRef() in the Event hierarchy to adoptRefWillBeRefCountedGarbageCollected()

I forgot to replace a couple of adoptRef() in r170164. This CL fixes them.

TBR=ager
BUG=340522

Review URL: https://codereview.chromium.org/212593012

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@170178 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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