These tests are added per bug 1251519 comment 10.
test_move_cursor_to_front_by_dragging_caret_to_front_br_element() covers
example 1, and test_drag_caret_from_front_to_end_across_columns() covers
example 3. Example 4 is not easy to write in marionette test since it's
difficult to know whether an image is selected.
Both tests will fail if we clamp the dragging point by using only the
text frame rects as the patch attached in bug 1251519 comment 7.
MozReview-Commit-ID: CKZQKGI6YUw
--HG--
extra : rebase_source : 72f5c2a960c2659fe5015a3ab488d4baa1918059
970a0bf203