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This implements WebServiceWorkerRegistration based on the latest spec
and resolves a register promise with it instead of a ServiceWorker object.

Spec: https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#service-worker-registration-obj 

[1] Blink: https://codereview.chromium.org/413123002/
[2] Chromium: This patch.
[3] Blink: Remove the macro and fix a bunch of layout tests.


BUG=396400
TEST=compile (tests will be added by subsequent patches)

Review URL: https://codereview.chromium.org/415963002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285599 0039d316-1c4b-4281-b951-d872f2087c98