Allow prolonged CanvasAsyncBlobCreator lifetime, avoid indirect leaks.
Weakly keeping this async object to avoid resource leaks is problematic
(r399445 + r399675), as the object must remain alive until completed.
Undo that experiment and instead keep the object alive until all its
posted tasks have been processed. But for the task that wins and
is processed first, have it clear out the heap references that
would otherwise keep heavy objects alive.
R=
BUG=
Review-Url: https://codereview.chromium.org/2065913003
Cr-Commit-Position: refs/heads/master@{#399856}
2 files changed
