Record document mode histogram in UMA on every upload.

chrome/browser/metrics/chrome_metrics_service_client.h

Index: chrome/browser/metrics/chrome_metrics_service_client.h
diff --git a/chrome/browser/metrics/chrome_metrics_service_client.h b/chrome/browser/metrics/chrome_metrics_service_client.h
index 1cb9f4536466cad07ccc362a12cb42e3950f5bdb..e7f260c945e99b2662956c304311b493ef716e0e 100644
--- a/chrome/browser/metrics/chrome_metrics_service_client.h
+++ b/chrome/browser/metrics/chrome_metrics_service_client.h
@@ -167,12 +167,6 @@ class ChromeMetricsServiceClient
   GoogleUpdateMetricsProviderWin* google_update_metrics_provider_;
 #endif
 
-#if !defined(OS_CHROMEOS) && !defined(OS_IOS)
-  // The SigninStatusMetricsProvider instance that was registered with
-  // MetricsService. Has the same lifetime as |metrics_service_|.
-  SigninStatusMetricsProvider* signin_status_metrics_provider_;
-#endif
-
   // Callback that is called when initial metrics gathering is complete.
   base::Closure finished_gathering_initial_metrics_callback_;