prometheus/prometheus — pull request #420 by juliusv (2014-12-10 02:53:05+00:00)
Title: Introduce copy-on-write for metrics in AST.

This depends on changes in:

https://github.com/prometheus/client_golang/tree/cow-metrics.

Change-Id: I80b94833a60ddf954c7cd92fd2cfbebd8dd46142