Remove dependency on SingleThreadedProxyResolver from resolve_proxy_msg_helper_unittest.cc.

Extracts MockAsyncProxyResolver to "mock_proxy_resolver.h".

This should be the last unittest that needs cleanup post r21631.

BUG=http://crbug.com/11079

Review URL: http://codereview.chromium.org/160619

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@22591 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed