GitLab

Extract SystemWebAppManager into CreateCommonSubsystems().

Fix comments.

Bug: 877898
Change-Id: I909f2c92317a2db2e0a73a1af08be28d84a51c03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1737492Reviewed-by: Alan Cutter <alancutter@chromium.org>
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684254}