Wire InstallFinished and add some InstallEvent.waitUntil tests

BUG=285976
TEST=content_browsertests:ServiceWorkerVersionBrowserTest.Install*

Review URL: https://codereview.chromium.org/153553008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250804 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250804