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https://crrev.com/c/2135054 resolved a threading issue by moving print
operations to the browser UI thread on Windows. Prior to that CL, the
work being done was marked as blocking at the task level, rather than
at the individual API level. The blocking annotations were removed in
order to not have a ScopedBlockingCall immediately preceded by a
ScopedAllowBlocking.

This CL reintroduces the ScopedBlockingCall marks at the point where
potentially blocking APIs are actually called. Existing callers also
gain ScopedAllowBlocking as needed.

Bug: 1067666
Change-Id: Ifb96feb96f0e6ba38ac06f09f0aa9640c547dba2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2128690
Commit-Queue: Kevin Babbitt <kbabbitt@microsoft.com>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756910}