[Web Payments] Add PopMany and Size functions to ViewStack

chrome/browser/ui/views/payments/view_stack.h

Index: chrome/browser/ui/views/payments/view_stack.h
diff --git a/chrome/browser/ui/views/payments/view_stack.h b/chrome/browser/ui/views/payments/view_stack.h
index 5b48c6de8c5dcbd5b102c6d8ca55a3fca10a9eec..8da22954d7321f8d13b72a0fcd1d1086285c04d9 100644
--- a/chrome/browser/ui/views/payments/view_stack.h
+++ b/chrome/browser/ui/views/payments/view_stack.h
@@ -33,6 +33,12 @@ class ViewStack : public views::BoundsAnimatorObserver,
   // it's properly deleted after the animation.
   void Pop();
 
+  // Removes |n| views from the stack but only animates the topmost one. The end
+  // result is an animation from the top-most view to the destination view.
+  void PopMany(int n);
+
+  size_t size() const;
+
   // views::View:
   // The children of this view must not be able to process events when the views
   // are being animated so this returns false when an animation is in progress.