DBus: Update PowerManagerClient to new pattern

This replaces calls to:
chromeos::PowerManagerClient::Initialize(nullptr)
with:
chromeos::PowerManagerClient::InitializeFake()

For mechanical changes:
TBR=sky@chromium.org

Bug: 647367
Change-Id: I1991255f98405f9a5fe1dd25cd9ab67754bd37c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1518908
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642033}
52 files changed