Encapsulate WebScopedVirtualTimePauser inside Blink

This moves history navigation virtual time pauser from
RenderViewImpl to Page, which has two benefits:
- slimming down RenderViewImpl;
- encapsulating virtual time inside Blink.

Most of changes are moving virtual time pauser creation
from thread scheduler to page scheduler.

Bug: none
Change-Id: I9fc2683e974e005d8cea35ced0f5f82931215b5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1856929
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705679}
20 files changed