Dispatch the ServiceWorker "activate" event during activation

This will be tested by a Chromium browsertest. Service Worker plumbing that would make this possible to test in Blink isn't fitted yet.

BUG=356021

Review URL: https://codereview.chromium.org/214413004

git-svn-id: svn://svn.chromium.org/blink/trunk@170310 bbb929c8-8fbe-4397-9dbb-9b2b20218538
MemoryCache: make sure that Resources are evicted only when they can be deleted

This CL fixes a problem where Resources can be taken out of the cache but not
deleted (if their handle count is not 0 for example).

BUG=290193

Review URL: https://codereview.chromium.org/179943002

git-svn-id: svn://svn.chromium.org/blink/trunk@170311 bbb929c8-8fbe-4397-9dbb-9b2b20218538