Hide call to removeDisplayTree in CueTimeline

TextTrack::setMode explicitly cleans out the display trees of its cues.
Move this into a new method - hideCues() - on CueTimeline and call that
instead. This keeps the manipulation of the display representation in a
single place.

BUG=321654

Review URL: https://codereview.chromium.org/994353003

git-svn-id: svn://svn.chromium.org/blink/trunk@191748 bbb929c8-8fbe-4397-9dbb-9b2b20218538
3 files changed
tree: dd96f13e6e1fd05b8a3abc17aa5f0c4908866101
  1. third_party/