Adding synthetic field trial for DataReductionProxyEnabled

components/metrics/metrics_service.h

Index: components/metrics/metrics_service.h
diff --git a/components/metrics/metrics_service.h b/components/metrics/metrics_service.h
index b0dcb82beaa053d5a89fbeed8fefffdb5f2e1f76..7171dc0d21df90763e225124a6960bd1d4d85af0 100644
--- a/components/metrics/metrics_service.h
+++ b/components/metrics/metrics_service.h
@@ -67,6 +67,8 @@ struct SyntheticTrialGroup {
   base::TimeTicks start_time;
 
  private:
+  // Synthetic field trial users:
+  friend class ChromeMetricsServiceAccessor;

[Alexei Svitkine (slow), 2014/07/30 19:00:32]

Can you change this to be MetricsServiceAccessor? (That is the class that is
already a friend of MetricsService and we're planning to move it to the
component, so it's OK to have it here.)

Then, a bit more plumbing unfortunately, but what you can then do is have
MetricsServiceAccessor have the code that uses this API in a protected function
that takes a MetricsService* param and then the public
ChromeMetricsServiceAccessor method simply call that method with
g_browser_process->metrics_service() as a param.

(Sorry for asking you to do this extra plumbing - but this is effectively the
first use of a synthetic trial and this bit of extra work is needed to expose
the API while whitelisting access to it through the component boundary.)

[megjablon, 2014/07/30 21:27:07]

Does this looks like what you want?

   friend class MetricsService;
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, RegisterSyntheticTrial);