Only dispose proxy-less WebServiceWorkerRegistration objects.

If a service worker registration is passed along to a resolver that's
in a detached/stopping state, the WebServiceWorkerRegistration is
simply disposed of.

Have that dispose step only delete the object if the registration object
isn't attached to a proxy already. If it is, it is responsible for
releasing the resource.

R=haraken
BUG=426321

Review URL: https://codereview.chromium.org/669423002

git-svn-id: svn://svn.chromium.org/blink/trunk@184288 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove last usage of kReturnToCache_FlagBit flag.

R=junov@chromium.org

Review URL: https://codereview.chromium.org/672943003

git-svn-id: svn://svn.chromium.org/blink/trunk@184289 bbb929c8-8fbe-4397-9dbb-9b2b20218538