Allow constructing {Interface,Struct}Ptr from nullptr

mojo/public/cpp/bindings/interface_ptr.h

Index: mojo/public/cpp/bindings/interface_ptr.h
diff --git a/mojo/public/cpp/bindings/interface_ptr.h b/mojo/public/cpp/bindings/interface_ptr.h
index c56e770e1eefb8547cd4035b95468121c2029cac..a2ede4d510b04c7f12fd59e8f4e08fd351893fe0 100644
--- a/mojo/public/cpp/bindings/interface_ptr.h
+++ b/mojo/public/cpp/bindings/interface_ptr.h
@@ -18,16 +18,22 @@ 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.internal_state_);
+    return *this;
+  }
+
+  InterfacePtr& operator=(decltype(nullptr)) {
     reset();
-    internal_state_.Swap(&other.object->internal_state_);
     return *this;
   }