The chromium-side backchannel plumbing for blobs in IDB.
This requires https://codereview.chromium.org/235933013/.

BUG=108012

Review URL: https://codereview.chromium.org/240003010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266677 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed