Misc. shortcuts cleanup:

* Eliminate using directives that don't save lines
* Add a helper to shorten a unittest
* No need to say ShortcutsBackend:: inside the ShortcutsBackend declaration
* Make more functions private
* Misc. small formatting changes

BUG=none
TEST=none
R=bartn@chromium.org, brettw@chromium.org

Review URL: https://codereview.chromium.org/27056006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228521 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228521