Add UMA Histogram Manager to Cronet.

components/metrics/metrics_log.h

Index: components/metrics/metrics_log.h
diff --git a/components/metrics/metrics_log.h b/components/metrics/metrics_log.h
index 53b30e63a79880d0357409ddbec336a816f80d6e..587b12e840d95bbdaebea5b718f24416230d16d8 100644
--- a/components/metrics/metrics_log.h
+++ b/components/metrics/metrics_log.h
@@ -141,6 +141,8 @@ class MetricsLog {
 
   LogType log_type() const { return log_type_; }
 
+  ChromeUserMetricsExtension* uma_proto() { return &uma_proto_; }
+
  protected:
   // Exposed for the sake of mocking/accessing in test code.
 
@@ -149,7 +151,6 @@ class MetricsLog {
   virtual void GetFieldTrialIds(
       std::vector<variations::ActiveGroupId>* field_trial_ids) const;
 
-  ChromeUserMetricsExtension* uma_proto() { return &uma_proto_; }
   const ChromeUserMetricsExtension* uma_proto() const {
     return &uma_proto_;
   }