The hermetic Xcode tooling in that repo is not yet easily usable for
Xcode 9. There are two main issues:
1. The tooling currently assumes that macOS host builds should use
Xcode 8, whereas iOS builds should use Xcode 9. Flutter builds should
use Xcode 9 in all cases.
2. The tooling currently includes a bail-out condition for iOS builds
that exits non-zero immediately (Chrome hasn't yet migrated its iOS
build to this tooling).
In the meantime, I've manually updated the bot infra with Xcode 9 and
we'll continue to use the current find_xcode.py tooling until Chrome's
new Mac/iOS tooling is ready.
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