Add the IndexedDBActiveBlobRegistry, currently unused, to enable future blob
support.

BUG=108012
R=cmumford,jsbell

Review URL: https://codereview.chromium.org/203833003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@261440 0039d316-1c4b-4281-b951-d872f2087c98
14 files changed