[Media Router] Add P1 UMA metrics for Media Router.

chrome/browser/media/router/media_router_dialog_controller.cc

Index: chrome/browser/media/router/media_router_dialog_controller.cc
diff --git a/chrome/browser/media/router/media_router_dialog_controller.cc b/chrome/browser/media/router/media_router_dialog_controller.cc
index 9efe8b98f0c2fb49839eb762bfc925d6a82833c0..f363730fe0a0a6ff014f7df935a34480c0c242cf 100644
--- a/chrome/browser/media/router/media_router_dialog_controller.cc
+++ b/chrome/browser/media/router/media_router_dialog_controller.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/media/router/media_router_dialog_controller.h"
 
+#include "chrome/browser/media/router/media_router_metrics.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_delegate.h"
@@ -85,6 +86,9 @@ bool MediaRouterDialogController::ShowMediaRouterDialogForPresentation(
   // Show the initiator holding the existing media router dialog.
   ActivateInitiatorWebContents();
 
+  media_router::MediaRouterMetrics::RecordMediaRouterDialogOrigin(
+      media_router::PAGE);
+
   return true;
 }