Part of <http://webkit.org/b/31414> Implement new SPI for dealing with
user scripts/stylesheets and isolated worlds

Reviewed by Sam Weinig.

WebCore:

Covered by existing tests.

* WebCore.base.exp: Update exported symbols to match what now exists
and is needed by WebKit.

* bindings/js/ScheduledAction.cpp:
(WebCore::ScheduledAction::execute): Updated for function rename.

* bindings/js/ScriptController.cpp: Removed code that dealt with
worldIDs.
(WebCore::ScriptController::createWorld): Added. Returns a new world
suitable for use on the main thread.
(WebCore::ScriptController::executeScriptInWorld): Renamed from
executeScriptInIsolatedWorld, since this works just fine with a
"normal" world.

* bindings/js/ScriptController.h: Added createWorld, removed functions
that took worldIDs, renamed executeScriptInIsolatedWorld to
executeScriptInWorld.

* page/Frame.cpp:
(WebCore::Frame::injectUserScripts):
(WebCore::Frame::injectUserScriptsForWorld):
Updated for changes to User...