Make ServiceWorkerVersion::{Start,Stop}Worker take callback

Also adds content_browsertests for start & stop flow

BUG=313530
TEST=content_browsertests:ServiceWorkerBrowserTest.\*

Review URL: https://codereview.chromium.org/145033012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247380 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed