Eliminate use of 'delete self' pattern in AttachmentUploaderImpl.

Eliminate use of 'delete self' pattern in AttachmentUploaderImpl.

Prior to this change UploadState objects would synchronously notify
AttachmentUploaderImpl that they were done and could be deleted.  This
meant they were still on the call stack when their destructor was
invoked.  While it worked, it was subtle and might lead to bugs in the
future.

BUG=

Committed: https://crrev.com/58c7a2f84240aa23775167f9df91b7dbed66e3d6
Cr-Commit-Position: refs/heads/master@{#294218}

[maniscalco, 2014-09-09 22:54:11]

maniscalco@chromium.org changed reviewers:
+ pavely@chromium.org

[maniscalco, 2014-09-09 22:57:23]

Pavel, would you please review this change?

This fixes a long standing issue with AUI.  It's currently not a problem, but
this will simplify things when I work on responding to network change events.

[pavely, 2014-09-10 00:25:43]

lgtm

[maniscalco, 2014-09-10 18:43:47]

The CQ bit was checked by maniscalco@chromium.org

[commit-bot: I haz the power, 2014-09-10 18:52:54]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/maniscalco@chromium.org/556083002/20001

[commit-bot: I haz the power, 2014-09-10 20:37:58]

Committed patchset #2 (id:20001) as 91c8b4f5295599709dfb981a11c074c07e52e0e6

[commit-bot: I haz the power, 2014-09-10 20:40:28]

Patchset 2 (id:??) landed as
https://crrev.com/58c7a2f84240aa23775167f9df91b7dbed66e3d6
Cr-Commit-Position: refs/heads/master@{#294218}