Change the UrlRequestJob base class to be thread safe because the sub class UrlRequestFileJob can be deleted on multiple threads.
Change the UrlRequestJob base class to be thread safe because the sub class UrlRequestFileJob can be deleted on multiple threads.

git-svn-id: http://src.chromium.org/svn/trunk/src@563 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: dddc517764bcda032d29819cc6fc4ac569f0cbcd
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