Use the media galleries controller interface for the scan result dialog.

chrome/browser/media_galleries/media_galleries_dialog_controller.h

Index: chrome/browser/media_galleries/media_galleries_dialog_controller.h
diff --git a/chrome/browser/media_galleries/media_galleries_dialog_controller.h b/chrome/browser/media_galleries/media_galleries_dialog_controller.h
index 01075807f984abaa93bfeebea7658ab81f8becf8..c8e016e86bf755351d7827e8e6ce0b2763fe1d65 100644
--- a/chrome/browser/media_galleries/media_galleries_dialog_controller.h
+++ b/chrome/browser/media_galleries/media_galleries_dialog_controller.h
@@ -31,6 +31,10 @@ class MediaGalleriesDialog {
   // Constructs a platform-specific dialog owned and controlled by |controller|.
   static MediaGalleriesDialog* Create(
       MediaGalleriesDialogController* controller);
+ private:
+  friend class TestMediaGalleriesAddScanResultsFunction;
+
+  virtual void AcceptDialogForTesting() = 0;
 };
 
 // Multiple dialog controllers are based on this interface.