Move MetricsService final log collection tasks to client.

components/metrics/metrics_service_client.h

Index: components/metrics/metrics_service_client.h
===================================================================
--- components/metrics/metrics_service_client.h	(revision 271878)
+++ components/metrics/metrics_service_client.h	(working copy)
@@ -8,6 +8,7 @@
 #include <string>
 
 #include "base/basictypes.h"
+#include "base/callback_forward.h"
 #include "components/metrics/proto/system_profile.pb.h"
 
 namespace metrics {
@@ -37,6 +38,11 @@
 
   // Returns the version of the application as a string.
   virtual std::string GetVersionString() = 0;
+
+  // Called prior to a metrics log being closed, allowing the client to collect
+  // extra histograms that will go in that log. Asynchronous API - the client
+  // implementation should call |done_callback| when complete.
+  virtual void CollectFinalMetrics(const base::Closure& done_callback) = 0;
 };
 
 }  // namespace metrics