GitLab

* Eliminate unused CYCLE_BACKWARD_LINEAR action -- linear cycling only goes
  forward.
* Consolidate the window cycling code into helper functions

BUG=none
TEST=ash_unittests Accelerator*

Review URL: https://chromiumcodereview.appspot.com/23654011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221430 0039d316-1c4b-4281-b951-d872f2087c98