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

ui/views/controls/scrollbar/native_scroll_bar.h

Index: ui/views/controls/scrollbar/native_scroll_bar.h
diff --git a/ui/views/controls/scrollbar/native_scroll_bar.h b/ui/views/controls/scrollbar/native_scroll_bar.h
index c9d96af77e7efc62bb73d52ccb3b49c175e03298..c94089514c3fdedc41ffc4a84ba7370fd2378658 100644
--- a/ui/views/controls/scrollbar/native_scroll_bar.h
+++ b/ui/views/controls/scrollbar/native_scroll_bar.h
@@ -18,6 +18,9 @@ class NativeTheme;
 }
 
 namespace views {
+namespace test {
+class ScrollViewTestApi;
+}
 
 class NativeScrollBarWrapper;
 
@@ -38,6 +41,7 @@ class VIEWS_EXPORT NativeScrollBar : public ScrollBar {
 
  private:
   friend class NativeScrollBarTest;
+  friend class test::ScrollViewTestApi;
   FRIEND_TEST_ALL_PREFIXES(NativeScrollBarTest, Scrolling);
 
   // Overridden from View.