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This CL fixes a potential race/bug in PrivacyScreenController where
the cached display snapshots in the display configurator (from which
we derive the internal display's id) may become invalidated while
SetPrivacyScreen() tasks are awaiting execution. For example, this may
happen when rapid display configuration events are triggered when a
device wakes up and is connected to one or more external displays.

In addition, this CL instrument drm_util.cc to help investigating
https://crbug.com/1105919.
Also see:
http://crash/browse?q=product_name%3D%27Chrome_ChromeOS%27+AND+expanded_custom_data.ChromeCrashProto.magic_signature_1.name%3D%27ui%3A%3ADrmNativeDisplayDelegate%3A%3ASetPrivacyScreen%27#productname:1000,productversion:30,magicsignature:50,magicsignature2:50,stablesignature:50,operatingsystemfamily:30,+devicemodel:40,magicsignaturesorted:50

Bug: 1105919
Change-Id: Ic3b6b86bc9a6f50a115e5ec563b4595ab5c24975
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2330891
Commit-Queue: Gil Dekel <gildekel@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797897}