GitLab

changes:
According to the design doc: go/cros-persistent-window-bounds, add UMA
for recording the number of windows restored for persistent window
restore in multi-display scenario.

Bug: 805046
Test: tested on device, checked chrome://histograms and added test coverage
Change-Id: I4f8c815c1b88dd605a02b509b27311d567998da1
Reviewed-on: https://chromium-review.googlesource.com/942186Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Qiang Xu <warx@google.com>
Cr-Commit-Position: refs/heads/master@{#540339}