The serviceworker update algo has to wait until documents close prior to performing...

The serviceworker update algo has to wait until documents close prior to performing its final activation step. If the browser exits prior to that happening, the algo has to be completed in the next browsing session. This CL adds logic that will trigger the deferred activation when first navigating into a registered scope.

This CL also adds logic to defer navigations into a registered scope while ACTIVATING and not yet ACTIVATED.

BUG=371671

Review URL: https://codereview.chromium.org/413853002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286146 0039d316-1c4b-4281-b951-d872f2087c98