Ensure that the WebstoreInstaller is always deleted on the UI thread

Ensure that the WebstoreInstaller is always deleted on the UI thread

The crash stacks show a CHECK failure when doing the unregistration due to
NotificationRegistrar deletion, indicating that the WebstoreInstaller is
getting deleted on a different thread from where the original notification
registration took place. This CL makes the ref counting infrastructure always
do the delete on the UI thread instead of whichever thread happened to do the
last Release, which should hopefully fix the problem.

BUG=125485
TEST=CHECK failures with a stack matching the signature in the bug report
should stop appearing


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=149646

[miket_OOO, 2012-08-02 15:53:55]

lgtm

http://codereview.chromium.org/10832105/diff/1/chrome/browser/extensions/webs...
File chrome/browser/extensions/webstore_installer.h (right):

http://codereview.chromium.org/10832105/diff/1/chrome/browser/extensions/webs...
chrome/browser/extensions/webstore_installer.h:33: class WebstoreInstaller
:public content::NotificationObserver,
I liked the old whitespace better.

[commit-bot: I haz the power, 2012-08-02 16:00:23]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/asargent@chromium.org/10832105/1

[commit-bot: I haz the power, 2012-08-02 17:23:52]

Change committed as 149646