WorkerGlobalScope: verify same-heap event listeners.

To help narrow down failures during tracing of a WorkerGlobalScope's
event listeners, verify that the listeners added belong to the
same heap as the WorkerGlobalScope itself.

R=
BUG=677654

Review-Url: https://codereview.chromium.org/2608113002
Cr-Commit-Position: refs/heads/master@{#441058}
1 file changed