Adding Writing direction to the context menu for linux gtk.

Blink side change is here https://codereview.chromium.org/66313007/

This CL takes care of the context menu on Linux Gtk. Most of the changes are copied from Writing direction context menu entry implementation on MacOSX. There seems to be no way to change writing direction on Aura. I would like create a separate CL to implement the same on Aura. 

BUG=91178
TBR=cpu@chromium.org

Review URL: https://codereview.chromium.org/73963004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236515 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236515