Mojo: share code between SyncDispatcher and Connector

R=piman@chromium.org

Review URL: https://codereview.chromium.org/185723003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254952 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254952