Introducing the WebServiceWorkerCacheStorage

A new WebServiceWorkerCacheStorage object is introduced for embedders to
implement the CacheStorage API.

While we have been developing ServiceWorker's CacheStorage API, the
underlying API has changed, and that's updated here as well.

See https://github.com/slightlyoff/ServiceWorker/issues/372 for a
discussion of the changes and motivations, and the spec at
https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#cache-storage
is up to date as of writing.

R=falken@chromium.org,abarth@chromium.org,jkarlin@chromium.org,jochen@chromium.org
BUG=392621

Review URL: https://codereview.chromium.org/424643002

git-svn-id: svn://svn.chromium.org/blink/trunk@179676 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Gardening: Update test expectations.

- The result of media/track/track-cue-rendering-horizontal.html on Snow Leopard
  looks minor renderling difference.  Mark it rebaseline.
- Update OilpanExpectations

BUG=400645,398472
TBR=jbroman@chromium.org

Review URL: https://codereview.chromium.org/448023002

git-svn-id: svn://svn.chromium.org/blink/trunk@179677 bbb929c8-8fbe-4397-9dbb-9b2b20218538