GitLab

Drive by changes:
- Mark blocking I/O functions with ScopedBlockingCall objects.
- Promote TaskPriority to USER_VISIBLE: icons are visible in UI.
- Promote TaskShutdownBehavior to BLOCK_SHUTDOWN: Web Apps metadata is critical.

This code is disabled by default behind kDesktopPWAsWithoutExtensions
base feature.

Bug: 1029221
Change-Id: Iaec0bb4b6ec97181ec0dad2326bcd249fd6d0ea9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1941449Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719875}