Fix inspector crash when reloading during a debugger pause on a page with unload event handlers

This was regressed in r155659.

BUG=279919
TEST=manually tested with repro in bug

Review URL: https://chromiumcodereview.appspot.com/23640006

git-svn-id: svn://svn.chromium.org/blink/trunk@157375 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Trigger `window.onerror` only for exceptions thrown in the same world.

This patch addresses half of crbug.com/225513 by grabbing the currently
active DOMWrapperWorld when creating ErrorEvent objects, and checking
that we're still in the same world when triggering `window.onerror`
handlers.

The next step will be to adjust event dispatching to ensure that 'error'
event listeners only trigger in the same world as the exception. I'll address
that in a separate patch; this patch adds several FAILing test results to make
that gap clear.

BUG=225513

Review URL: https://chromiumcodereview.appspot.com/21071003

git-svn-id: svn://svn.chromium.org/blink/trunk@157376 bbb929c8-8fbe-4397-9dbb-9b2b20218538