Mojo C++ bindings: more consistent Clone() and Equals().

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 e427dc4668d2a273b85f3cb4706f7db781f8daa1..041c24264147084046654e4a41905f9b95d7a537 100644
--- a/mojo/public/cpp/bindings/interface_ptr.h
+++ b/mojo/public/cpp/bindings/interface_ptr.h
@@ -183,6 +183,15 @@ class InterfacePtr {
     return internal_state_.associated_group();
   }
 
+  bool Equals(const InterfacePtr& other) const {
+    if (this == &other)
+      return true;
+
+    // Now that the two refer to different objects, they are equivalent if
+    // and only if they are both null.
+    return !(*this) && !other;
+  }
+
   // DO NOT USE. Exposed only for internal use and for testing.
   internal::InterfacePtrState<Interface, Interface::PassesAssociatedKinds_>*
   internal_state() {