GitLab

This also fixes a few bugs in the IDB/Blob stuff:
* Removed a DCHECK that could hit depending on test teardown order.
* Made ChainedBlobWriterImpl truly asynchronous, fixing a crash if a File write failed before the first Blob write was attempted.
* Fix a crash where we'd try to free a scoped_ptr twice in the event of an abort.

Note that most of the time we won't actually receive File metadata, as Files often aren't snapshotted; I've got a blink change in progress [https://codereview.chromium.org/325383002/] that will always send it.

BUG=

Review URL: https://codereview.chromium.org/333533002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278509 0039d316-1c4b-4281-b951-d872f2087c98