Fix misuses of CrossThreadBind in AnimationWorkletMutatorDispatcherImpl

Straightforward replacement. CrossThreadBind was being used for passing
callback instances to functions that were expecting "Once callbacks".

BUG=963574
R=haraken@chromium.org, hiroshige@chromium.org

Change-Id: I9769928fca124d890163bd0c464b5a0b92ae7fca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1621390
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#661898}
3 files changed