Introduce a SchedulerHelper in content/child/scheduler
We are planning on adding a WorkerScheduler for blink worker threads,
which will reuse much of the RendererScheduler logic for posting
Default and IdleTask tasks.
This patch pulls out the common logic into a SchedulerHelper
(We're going to think of a better name for this) and moves a bunch of
dependencies into a new content/child/scheduler directory where the WorkerScheduler
will be added in https://codereview.chromium.org/
1033643004/
A WorkerSceduler is a pre-requisite for refactoring away the Blink
Timer Heap as described in:
https://docs.google.com/document/d/163ow-1wjd6L0rAN3V_U6t12eqVkq4mXDDjVaA4OuvCA/edit?usp=sharing
BUG=463143
Review URL: https://codereview.chromium.org/
1025323003
Cr-Commit-Position: refs/heads/master@{#323214}