Pausable Object cleanup - FontFaceSet

FontFaceSet doesn't need to be a pausable object to avoid dispatching
events when paused since:
- workers don't pause objects
- events queued in the kInternalDefault queue are already pausable.

BUG=907125

Change-Id: I3dc4c392ecad42f2f008837298ed5e7f7afb274d
Reviewed-on: https://chromium-review.googlesource.com/c/1368448
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615277}
6 files changed