Instead of using long_press_without_contextmenu() with built-in long tap
injector in AccessibleCaretEventHub to select a word, we can use
DOMWindowUtis to send synthesized mouse long tap events to gecko. This
triggers the code path which is closer to the real events fired by APZ
on B2G.
This change also makes marionette tests cover the focus-changing code by
long tap in AccessibleCaretManager. This is subtle but significant since
it's possible to write focus changing tests via long tap now.
--HG--
extra : commitid : 88Mi3beYfSI
extra : rebase_source : e61d6341a88b56e1c186e53d361b46f35e78f758
ef28c788e2