This patch introduces a new way to way to schedule input tasks, such
that input tasks remain at `InputHigh` priority normally, however, when
there's a pending `Vsync` priority task in the task queue, we
increase the priority of input tasks from `InputHigh` to `InputHighest` to
rush processing the pending input tasks.
There are two restrictions to ensure we don't delay vsync too much:
- There's a hard limit duration
- We won't process the input tasks that are newly added after we've
started to process the current number of input tasks
Differential Revision: https://phabricator.services.mozilla.com/D109499
25b542e9e1