It is owned by URLRequestStreamJob on the IO thread once request starts,
but if the ownership was abondoned while transfering it to IO thread
which is possible when a request is aborted, then we need to make sure
its destroyed on the right thread to avoid lock in v8.
* Use weak pointer to avoid race condition
* Use DeleteSoon to delete pointer across threads
* Simplify EventSubscriber
* No need to manually mange V8 convertions
* Fix cpplint warning
We should update cpplint for this, but let's do it in other PR.
* Move UI thread operations to EventSubscriber
* Less and more assertions
Some methods are now private so no more need to assert threads.
* Fix cpplint warnings
* No longer needs the EventEmitted
* EventSubscriber => StreamSubscriber
* Reduce the copies when passing data
* Fix cpplint warnings
