Release GetFileSystemRootPath callback on the correct thread.
Release GetFileSystemRootPath callback on the correct thread.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/4142009

git-svn-id: http://src.chromium.org/svn/trunk/src@64304 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 1c7cc8273536a834c8a45c2a42a79bb064039d37
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