Adds more to viewmanager

mojo/services/view_manager/node_delegate.h

Index: mojo/services/view_manager/node_delegate.h
diff --git a/mojo/services/view_manager/node_delegate.h b/mojo/services/view_manager/node_delegate.h
index 3e34940ffca0c7f3cda54c629613b387e1371062..5cec703818b7bea09942550588fbb09340664160 100644
--- a/mojo/services/view_manager/node_delegate.h
+++ b/mojo/services/view_manager/node_delegate.h
@@ -12,6 +12,7 @@ namespace services {
 namespace view_manager {
 
 struct NodeId;
+struct ViewId;
 
 class MOJO_VIEW_MANAGER_EXPORT NodeDelegate {
  public:
@@ -20,6 +21,11 @@ class MOJO_VIEW_MANAGER_EXPORT NodeDelegate {
                                       const NodeId& new_parent,
                                       const NodeId& old_parent) = 0;
 
+  // Invoked when the View associated with a node changes.
+  virtual void OnNodeViewReplaced(const NodeId& node,
+                                  const ViewId& new_view_id,
+                                  const ViewId& old_view_id) = 0;
+
  protected:
   virtual ~NodeDelegate() {}
 };