Oilpan: trace RenderVTTCue's cue back reference.

With RenderVTTCue on the heap, no need to keep a raw pointer
back to the VTTCue of its element.

R=haraken
BUG=340522

Review URL: https://codereview.chromium.org/806483002

git-svn-id: svn://svn.chromium.org/blink/trunk@187097 bbb929c8-8fbe-4397-9dbb-9b2b20218538
2 files changed
tree: f24434e98393df44fec31396852b974f02bdd1c8
  1. third_party/