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This new object is implemented in content in both the renderer and browser
side. The CacheStorage API methods now pass in to the browser process in
the UI thread, where all API calls are failed as not implemented.

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

Review URL: https://codereview.chromium.org/379303002

Cr-Commit-Position: refs/heads/master@{#288413}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288413 0039d316-1c4b-4281-b951-d872f2087c98