Add network information to UKM

Setup metric providers for UKM logs, and add network as a first client.
Small refactor of ChromeMetricsServiceClient::Initialize to put the registrations in their own methods.

BUG=678682

Review-Url: https://codereview.chromium.org/2671603002
Cr-Commit-Position: refs/heads/master@{#448330}
diff --git a/chrome/browser/metrics/chrome_metrics_service_client.h b/chrome/browser/metrics/chrome_metrics_service_client.h
index 11dff40f..6f12e37 100644
--- a/chrome/browser/metrics/chrome_metrics_service_client.h
+++ b/chrome/browser/metrics/chrome_metrics_service_client.h
@@ -102,6 +102,14 @@
   // Completes the two-phase initialization of ChromeMetricsServiceClient.
   void Initialize();
 
+  // Registers providers to the MetricsService. These provide data from
+  // alternate sources.
+  void RegisterMetricsServiceProviders();
+
+  // Registers providers to the UkmService. These provide data from alternate
+  // sources.
+  void RegisterUKMProviders();
+
   // Callback to chain init tasks: Pops and executes the next init task from
   // |initialize_task_queue_|, then passes itself as callback for each init task
   // to call upon completion.