Register OilPan thread interruptors on the main thread and in workers.

Ensure that WorkerThread is attached to the OilPan heap and WorkerRunLoop has safepoints in the right spots.

These changes together guarantee that no matter which thread attempts to GC other attached threads will arrive to safepoint and be stopped. If thread is looping inside V8 JIT compiled code it will be interrupted as well through the V8 API.

This completes OilPan threading infrustructure. All code is guarded with conditional compilation under ENABLE(OILPAN).

BUG=
R=abarth@chromium.org, ager@chromium.org, haraken@chromium.org

Review URL: https://codereview.chromium.org/144113002

git-svn-id: svn://svn.chromium.org/blink/trunk@165549 bbb929c8-8fbe-4397-9dbb-9b2b20218538