Oilpan: Replace most of RefPtrs of Event objects with oilpan's transition types

- Basically, this CL does the following three things:

(1) Replace PassRefPtr<xxxEvent> with PassRefPtrWillBeRawPtr<xxxEvent>.

(2) Replace RefPtr<xxxEvent> in on-heap objects with RefPtrWillBeMember<xxxEvent>.

(3) Replace RefPtr<xxxEvent> in off-heap objects with RefPtrWillBePersistent<xxxEvent>.

- This CL is not replacing any raw pointers with Members/Persistents, so it won't produce new memory leaks.

- This CL uses ListHashSet<Persistent<Event>> for DOMWindowEventQueue::m_queuedEvents, because HeapListHashSet is not yet implemented.

- This CL uses Deque<Persistent<Event>> for WebSocket::m_events, because HeapDeque is not yet implemented.

- In follow-up CLs, I will move more Event related objects to the heap and reduce Persistent handles introduced in this CL.

BUG=340522

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170733

Review URL: https://codereview.chromium.org/216523002

git-svn-id: svn://svn.chromium.org/blink/trunk@170769 bbb929c8-8fbe-4397-9dbb-9b2b20218538