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Many developers have added utility functions to check if the many Mojo
instances are ready and with the correct version, which seems redundant.
This change adds a function to do that (and log failures).

BUG=647853
TEST=cheets_SettingsBridge

Review-Url: https://codereview.chromium.org/2347293002
Cr-Commit-Position: refs/heads/master@{#419471}