This is a follow up on crrev.com/38f2e322

This CL does several things*:
- It greatly simplify the logic in SwapThrashingMonitorDelegateWin: As
  suggested by wez@ the observation window now looks at how many samples
  are above a certain threshold rather than looking at the average
  page-fault rate over an interval of time. This average rate was really
  affected by the small burst in paging and this was causing a lot of
  unwanted switch to the suspected state. The delta on this CL isn't
  displayed properly, swap_thrashing_monitor_win.h has been renamed to
  swap_thrashing_monitor_delegate_win.h and the SampleWindow subclass
  now replace the PageFaultAverageRate one.
- It introduce the monitor that owns this delegate. The monitor is
  responsible of calling the delegate at regular intervals to sample the
  state of the system.
- It emits some new metrics to record how much time is spent in each
  state and how often the system transition from one step to another.

* Sorry for sending this a one big CL... The timezone difference will
really slow down the release of this if I split it into too many
smaller CLs (and there's only a few days left for me to work on this).

Bug: 771478
TBR: chrisha@chromium.org
Change-Id: I8aa5c8fd2c768a3e1ad0c387a67c7205db5da37a
Reviewed-on: https://chromium-review.googlesource.com/738072


Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512398}