GitLab

Allow concurrent installs.
WebAppInstallManager owns all install tasks.

This CL introduces no behavior changes.

Bug: 901226
Change-Id: Ib231faeb7b3749f3f68436ac01d872075c4e6cb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1556659Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649322}