Move PPB_KeyboardInputEvent.GetCode to stable.

Remove GetUsbKeycode and SetUsbKeyCode since they were earlier verisons of this API that are not being used anywhere.

Remove all the KeyboardEvent _Dev files since they will no longer be used once GetCode is moved out.

BUG=286359,284774,275049
R=binji@chromium.org, dcheng@chromium.org, dmichael@chromium.org

Review URL: https://codereview.chromium.org/112983005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247275 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247275