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This CL makes two previously-asynchronous API functions synchronous,
which drastically improves the ease of using this class.

The two functions are GetHostStatus() and GetFeatureStates(). With this
CL, the class now caches the most recent value received from the service
and returns in synchronously. If the service's values change, the
changes will be reflected in the client class.

This change unblocks several sub-tasks which use the client, including
setup code for EasyUnlock, Instant Tethering, and AWM.

Bug: 875980, 824568
Change-Id: I29430f614ce17206692b916d66b0cf57ec09f636
Reviewed-on: https://chromium-review.googlesource.com/1196030Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587654}