DevTools: prepare EventBinding for processing events from multiple threads

This extracts most of the contents of WebInspector.TracingModel.EventBindings._init()
into _processMainThreadEvents() and moves its state into the class members, so we can
interleave processing of events from different threads.

BUG=361045

Review URL: https://codereview.chromium.org/292813009

git-svn-id: svn://svn.chromium.org/blink/trunk@174675 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Oilpan: Replace RefPtrs to Node and its subclasses in core/xml/ with Oilpan transition types.

This CL replaces RefPtrs in DOMImplementation because DOMParser uses
DOMImplementation.

BUG=357163

Review URL: https://codereview.chromium.org/288343017

git-svn-id: svn://svn.chromium.org/blink/trunk@174676 bbb929c8-8fbe-4397-9dbb-9b2b20218538