MacViews: Fix scrolling when clicking on the views::ScrollView scroll track

ui/views/controls/scrollbar/base_scroll_bar.h

Index: ui/views/controls/scrollbar/base_scroll_bar.h
diff --git a/ui/views/controls/scrollbar/base_scroll_bar.h b/ui/views/controls/scrollbar/base_scroll_bar.h
index 6d6944259d34894737e2a9369a1f839650fc137f..b56663dc82566a7946173b85f464608de19c921a 100644
--- a/ui/views/controls/scrollbar/base_scroll_bar.h
+++ b/ui/views/controls/scrollbar/base_scroll_bar.h
@@ -15,6 +15,9 @@
 #include "ui/views/repeat_controller.h"
 
 namespace views {
+namespace test {
+class ScrollViewTestApi;
+}
 
 class BaseScrollBarThumb;
 class MenuRunner;
@@ -114,6 +117,8 @@ class VIEWS_EXPORT BaseScrollBar : public ScrollBar,
   virtual int GetScrollIncrement(bool is_page, bool is_positive);
 
  private:
+  friend class test::ScrollViewTestApi;
+
   FRIEND_TEST_ALL_PREFIXES(NativeScrollBarTest, ScrollBarFitsToBottom);
   FRIEND_TEST_ALL_PREFIXES(NativeScrollBarTest, ThumbFullLengthOfTrack);
   int GetThumbSizeForTest();