When the carets are scrolled by APZ, they will hide and dispatch a
"visibilitychange" reason. The floating toolbar (ActionBarHandler.js) on
Android listens to the event to update its visibility.
Now we want to show carets continuously when scrolling the page, so it
make no sense to dispatch a "visibilitychange" reason. However we still
need to notify the toolbar that the carets are scrolling by apz.
Therefore, we need a this new "scroll" reason. It will be dispatch in
AccessibleCaretManager::OnScrollStart() in Part 2.
MozReview-Commit-ID: F9znxHV3xCZ
--HG--
extra : rebase_source : 89914ebe5ed4cbcb5a3fd792a9f260e4c389fe84
The old SelectionStateChangedEvent dispatched by SelectionChanged had
this field, but it has not being ported to CaretStateChangedEvent. We
should include selected text in the event so that Gaia could have a
chance to enhance user experience.
--HG--
extra : rebase_source : 7304b71e251e2ee081192340b8f86f22bf6e03a6
Ting-Yu Lin
Mark Capella
Jeremy Chen
Morris Tseng
Ryan VanderMeulen