Fixes crash in view_manager_lib

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

Index: mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.cc
diff --git a/mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.cc b/mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.cc
index be24cec1828ad1f8092c783d11cb17e0aceb1c77..82a9fd598cba89d7ca114f2dfeb66f67487f6a5a 100644
--- a/mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.cc
+++ b/mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.cc
@@ -447,6 +447,9 @@ ViewManagerSynchronizer::ViewManagerSynchronizer(ViewManagerDelegate* delegate)
 }
 
 ViewManagerSynchronizer::~ViewManagerSynchronizer() {
+  // Destroying the |view_manager_| may attempt to add transactions to
+  // |pending_transactions_|. So we need to destroy |view_manager_| first.
+  view_manager_.reset();
 }
 
 TransportNodeId ViewManagerSynchronizer::CreateViewTreeNode() {