This is one of a series of CLs adding a new metric type, EventMetric, which
is used for tracking numerical distributions.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=132103552
Add additional logic to handle cases when a MetricDescriptor is already defined
on the server, fix an NPE in related code, and add additional tests to ensure
that TimeSeries created from native MetricPoints are well-formed.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=130555708