If DeviceMetricsReportingEnabled is not set, there is some weird behavior:

1) We aren't sure whether UMA is enabled or not
2) The settings UI falls back into "you have to be the owner to set this setting" state, but with some bugs (empty dialogs, etc).

CPanel shows "Always send metrics to Google" by default (even if this policy is unset), so we should honor that description by sending up metrics even if the policy is unset.

I think the best way to do this is to add code to DevicePolicyDecoderChromeOS::DecodeGenericPolicies to set the policy to true if it's unset.