Map new subtrees when they are attached to the node hierarchy visible to a connection.

mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.h

Index: mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.h
diff --git a/mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.h b/mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.h
index 1a505836977093127944711cc405b537b19f3a5c..7a82a444e1ce5b801c1cafe25e60a1fc332f6529 100644
--- a/mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.h
+++ b/mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.h
@@ -6,6 +6,7 @@
 #define MOJO_SERVICES_PUBLIC_CPP_VIEW_MANAGER_LIB_VIEW_MANAGER_SYNCHRONIZER_H_
 
 #include "base/basictypes.h"
+#include "base/callback.h"
 #include "base/memory/scoped_vector.h"
 #include "base/memory/weak_ptr.h"
 #include "mojo/services/public/cpp/view_manager/view_manager_types.h"
@@ -48,6 +49,13 @@ class ViewManagerSynchronizer : public IViewManagerClient {
 
   void SetActiveView(TransportNodeId node_id, TransportViewId view_id);
 
+  void set_changes_acked_callback(const base::Callback<void(void)>& callback) {
+    changes_acked_callback_ = callback;
+  }
+  void ClearChangesAckedCallback() {
+    changes_acked_callback_ = base::Callback<void(void)>();
+  }
+
  private:
   friend class ViewManagerTransaction;
   typedef ScopedVector<ViewManagerTransaction> Transactions;
@@ -94,6 +102,8 @@ class ViewManagerSynchronizer : public IViewManagerClient {
   // construction.
   base::RunLoop* init_loop_;
 
+  base::Callback<void(void)> changes_acked_callback_;
+
   IViewManagerPtr service_;
 
   DISALLOW_COPY_AND_ASSIGN(ViewManagerSynchronizer);