Added check for null delegate when a socket stream closes between DoResolveHost and DoResolveHostDone.

      BUG=51846
TEST=None
Review URL: http://codereview.chromium.org/3145010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@56076 0039d316-1c4b-4281-b951-d872f2087c98