Allow constructing {Interface,Struct}Ptr from nullptr

mojo/public/cpp/bindings/interface_ptr.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_INTERFACE_PTR_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_INTERFACE_PTR_H_
 
 #include <algorithm>
 
 #include "mojo/public/cpp/bindings/error_handler.h"
 #include "mojo/public/cpp/bindings/lib/interface_ptr_internal.h"
 #include "mojo/public/cpp/environment/environment.h"
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
 class ErrorHandler;
 
 // InterfacePtr represents a proxy to a remote instance of an interface.
 template <typename Interface>
 class InterfacePtr {
-  MOJO_MOVE_ONLY_TYPE_FOR_CPP_03(InterfacePtr, RValue)
+  MOJO_MOVE_ONLY_TYPE(InterfacePtr)
  public:
   InterfacePtr() {}
+  InterfacePtr(decltype(nullptr)) {}
 
-  InterfacePtr(RValue other) {
-    internal_state_.Swap(&other.object->internal_state_);
+  InterfacePtr(InterfacePtr&& other) {
+    internal_state_.Swap(&other.internal_state_);
   }
-  InterfacePtr& operator=(RValue other) {
+  InterfacePtr& operator=(InterfacePtr&& other) {
     reset();
-    internal_state_.Swap(&other.object->internal_state_);
+    internal_state_.Swap(&other.internal_state_);
     return *this;
   }
 
+  InterfacePtr& operator=(decltype(nullptr)) {
+    reset();
+    return *this;
+  }
+
   ~InterfacePtr() {}
 
   Interface* get() const { return internal_state_.instance(); }
   Interface* operator->() const { return get(); }
   Interface& operator*() const { return *get(); }
 
   void reset() {
     State doomed;
     internal_state_.Swap(&doomed);
   }
@@ skipping 81 matching lines @@
     const MojoAsyncWaiter* waiter = Environment::GetDefaultAsyncWaiter()) {
   InterfacePtr<Interface> ptr;
   if (handle.is_valid())
     ptr.Bind(handle.Pass(), waiter);
   return ptr.Pass();
 }
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_INTERFACE_PTR_H_