Downstream users who use gRPC rather than REST don't want to pull down
rest-related dependencies.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=145834701
This change enforces URL-like metric names to match the behavior of
Stackdriver. The StackdriverWriter no longer prepends a slash, which was a
crutch.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=130537347