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This allows the hardware_class field in UMA to be populated on
iOS (with values like "iPhone9,3"), which will allow us to stop
sending those strings in the cpu_architecture field which is
what's currently being done.

BUG=370104

Review-Url: https://codereview.chromium.org/2860663005
Cr-Commit-Position: refs/heads/master@{#469499}