Async Cookies: Expose oncookiechange on ServiceWorkerGlobalScope.

cookiechange events have been dispatched to ServiceWorkerGlobalScope
since https://crrev.com/c/979334 landed, and can be observed using
addEventListener, as shown by the WPT test at
cookie-store/serviceworker_cookieStore_subscriptions_basic.tentative.https.html

This CL adds the oncookiechange attribute to ServiceWorkerGlobalScope,
allowing the event to be handled by a DOM0-style event handler.

Bug: 729800
Change-Id: Ic27979d94934abf833c116787cdad5243422324b
Reviewed-on: https://chromium-review.googlesource.com/1123766
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572400}
18 files changed