Simplify synchronous fetching in WebsitePermissionsFetcher.

This makes it easier to implement a synchronous
WebsitePermissionsFetcher.Task by simply overriding Task.run(), instead
of having to call TaskQueue.next() at the end.

Review URL: https://codereview.chromium.org/1536893002

Cr-Commit-Position: refs/heads/master@{#366404}
1 file changed