WebApp: Remove kInvalid from InstallSource enum.

- Remove kInvalid from InstallSource enum.
- Remove InstallOptions::InstallOptions default ctor.
- Rename InstallSource::kInternal to InstallSource::kInternalDefault
to match WebappInstallSource::INTERNAL_DEFAULT.

TBR=azeemarshad@chromium.org

Bug: 860583
Change-Id: I7d54d4585ada28a7a9e43e35f897de24974759e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1707895
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Reviewed-by: calamity <calamity@chromium.org>
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#678595}
22 files changed