Added standard gamepad mappings for Dualshock 4 on Mac and Linux.

R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/143713002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246111 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246111