Remove DOMWindowLifecycleObserver

DOMWindowLifecycleObserver is used just to notify the observers of
addition/removal of event listeners. The observers are not interested
in observing lifecycle of DOMWindow at all. Hence, this CL removes
DOMWindowLifecycleObserver by replacing it with simple inheritance
of LocalDOMWindow::EventListenerObserver.

BUG=610176

Review-Url: https://codereview.chromium.org/2134063002
Cr-Commit-Position: refs/heads/master@{#404644}
12 files changed