Add end to end test for Media galleries scan API.

chrome/browser/media_galleries/media_galleries_scan_result_dialog_controller.h

Index: chrome/browser/media_galleries/media_galleries_scan_result_dialog_controller.h
diff --git a/chrome/browser/media_galleries/media_galleries_scan_result_dialog_controller.h b/chrome/browser/media_galleries/media_galleries_scan_result_dialog_controller.h
index 96d87b694931b687c61455b0d58bd40a3961f109..8f004b0e755b04b19f522c3fe99c2f607f896b29 100644
--- a/chrome/browser/media_galleries/media_galleries_scan_result_dialog_controller.h
+++ b/chrome/browser/media_galleries/media_galleries_scan_result_dialog_controller.h
@@ -42,6 +42,11 @@ class MediaGalleriesScanResultDialog {
   // Constructs a platform-specific dialog owned and controlled by |controller|.
   static MediaGalleriesScanResultDialog* Create(
       MediaGalleriesScanResultDialogController* controller);
+
+ private:
+  friend class TestMediaGalleriesAddScanResultsFunction;
+
+  virtual void AcceptDialogForTesting() = 0;
 };
 
 // The controller is responsible for handling the logic of the dialog and
@@ -124,6 +129,7 @@ class MediaGalleriesScanResultDialogController
  private:
   friend class MediaGalleriesScanResultDialogControllerTest;
   friend class MediaGalleriesScanResultDialogCocoaTest;
+  friend class TestMediaGalleriesAddScanResultsFunction;
 
   // Bottom half of constructor -- called when |preferences_| is initialized.
   void OnPreferencesInitialized();