ServiceWorker: Implement updatefound event and version attributes (Chromium)

ServiceWorker: Implement updatefound event and version attributes (Chromium)

Changes in the renderer side:
* Implementing WebServiceWorkerRegistrationImpl in order to handle 'updatefound'
event and version attributes.
* Adding ServiceWorkerRegistrationHandleReference which is responsible for
incrementing/decrementing the refcount of ServiceWorkerRegistration in the
browser-side (in the same way as ServiceWorkerHandleRefernce).

Changes in the browser side:
* Adding ServiceWorkerRegistrationHandle which manages the refcount of
ServiceWorkerRegistration and listens to its version change events.
This is managed by ServiceWorkerDispatcherHost.

Changes in the wiring part:
* Adding new IPC messages for refcount operations.
* Changing Registered and SetVersionAttributes messages to carry the
registration handle id.

BUG=384119, 396400
TEST=content_unittests --gtest_filter=ServiceWorker*
TEST=run_webkit_tests.py --debug http/tests/serviceworker
TEST=https://codereview.chromium.org/466723002/ (layout tests for ServiceWorkerRegistration)
NOTRY=true

Review URL: https://codereview.chromium.org/463013002

Cr-Commit-Position: refs/heads/master@{#289415}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289415 0039d316-1c4b-4281-b951-d872f2087c98