Fixed IndexedDB blob retention

Fixed IndexedDB blob retention

R=michaeln
BUG=457536
Committed: https://crrev.com/24dc5eece51abf42b79c885573abc782c413945f
Cr-Commit-Position: refs/heads/master@{#315885}

[dmurph, 2015-02-11 21:43:22]

Hey Michael,

I made some stuff fail due to not quite getting the blob builder refactor right.
 Previously, we always created the shareable file references when people use
AddFinishedBlob.  After the refactor this wasn't done unless the client
explicitly used that new method.

This change makes it so that all builder create the file reference whenever
someone adds a file.  I could change this to be handled internally within
BlobStorageContext, where it modifies the BlobItem given to it by the builder. 
Since this would cause the builder to also contain that file reference, I went
with this approach instead, and documented what happens in the method signature.

WDYT?

Thanks,
Daniel

[michaeln, 2015-02-11 23:20:27]

lgtm

[dmurph, 2015-02-11 23:22:21]

The CQ bit was checked by dmurph@chromium.org

[commit-bot: I haz the power, 2015-02-11 23:22:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/913303002/1

[commit-bot: I haz the power, 2015-02-12 00:31:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-12 00:32:37]

Patchset 1 (id:??) landed as
https://crrev.com/24dc5eece51abf42b79c885573abc782c413945f
Cr-Commit-Position: refs/heads/master@{#315885}