Don't call RemoveDestructionObserver on non-IO thread.
Don't call RemoveDestructionObserver on non-IO thread.

RemoveDestructionObserver is expected to be called on the IO thread.
Instead, just checking io_loop_ is NULL in destructor.
IO thread should be deleted and call WillDestroyCurrentMessageLoop() before deleting singletons in AtExitManager.

BUG=28526,28769
TEST=none

Review URL: http://codereview.chromium.org/460067

git-svn-id: http://src.chromium.org/svn/trunk/src@34655 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 7f6672ffafaeecb06bd59622ec37bd07b0b6d003
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser