Mojo C++ Bindings: Eliminate unbound ThreadSafeInterfacePtr

mojo/public/cpp/bindings/associated_interface_ptr.h

Index: mojo/public/cpp/bindings/associated_interface_ptr.h
diff --git a/mojo/public/cpp/bindings/associated_interface_ptr.h b/mojo/public/cpp/bindings/associated_interface_ptr.h
index 42cb9dc68e5e5426436f98b29ec791a27dc4af65..3ba8ccc213289f7f77d21dec6a0426e475b38c82 100644
--- a/mojo/public/cpp/bindings/associated_interface_ptr.h
+++ b/mojo/public/cpp/bindings/associated_interface_ptr.h
@@ -31,6 +31,8 @@ namespace mojo {
 template <typename Interface>
 class AssociatedInterfacePtr {
  public:
+  using PtrInfoType = AssociatedInterfacePtrInfo<Interface>;
+
   // Constructs an unbound AssociatedInterfacePtr.
   AssociatedInterfacePtr() {}
   AssociatedInterfacePtr(decltype(nullptr)) {}