Move VirtualTimePauser from LocalFrameClientImpl to FrameLoader

LocalFrameClientImpl is a glue class, it should not do any work
in DispatchXXX methods - this makes refactoring them difficult.

FrameLoader knows best about navigations and can control virtual
time pauser itself.

Bug: 855189
Change-Id: I8947146b593f5dd356f7edcd439961f8a731a2f1
Reviewed-on: https://chromium-review.googlesource.com/c/1267735
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598019}
5 files changed