Make MetricsService upload logs through an interface.

chrome/browser/metrics/chrome_metrics_service_client.h

Index: chrome/browser/metrics/chrome_metrics_service_client.h
===================================================================
--- chrome/browser/metrics/chrome_metrics_service_client.h	(revision 274045)
+++ chrome/browser/metrics/chrome_metrics_service_client.h	(working copy)
@@ -48,6 +48,10 @@
       const base::Closure& done_callback) OVERRIDE;
   virtual void CollectFinalMetrics(const base::Closure& done_callback)
       OVERRIDE;
+  virtual scoped_ptr<metrics::MetricsLogUploader> CreateUploader(
+      const std::string& server_url,
+      const std::string& mime_type,
+      const base::Callback<void(int)>& on_upload_complete) OVERRIDE;
 
   MetricsService* metrics_service() { return metrics_service_.get(); }