Implement WebThread::{add,remove}TaskObserver.

Depends on http://trac.webkit.org/changeset/101418

Review URL: http://codereview.chromium.org/8586038

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113010 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed