Emit substitution functions on Object.

sdk/lib/_internal/compiler/implementation/js_backend/native_emitter.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 class NativeEmitter {
 
   CodeEmitterTask emitter;
   CodeBuffer nativeBuffer;
@@ skipping 458 matching lines @@
     // Because of native classes, we have to generate some is checks
     // by calling a method, instead of accessing a property. So we
     // attach to the JS Object prototype these methods that return
     // false, and will be overridden by subclasses when they have to
     // return true.
     void emitIsChecks() {
       for (ClassElement element in
                Elements.sortedByPosition(emitter.checkedClasses)) {
         if (!requiresNativeIsCheck(element)) continue;
         if (element.isObject(compiler)) continue;
+        // Add function for the is-test.
         String name = backend.namer.operatorIs(element);
         addProperty(name,
             js.fun([], js.return_(js['false'])));
+        // Add a function for the (trivial) substitution.
+        addProperty(backend.namer.substitutionName(element),
+                    js.fun([], js.return_(js['null'])));
       }
     }
     emitIsChecks();
 
     jsAst.Expression makeCallOnThis(String functionName) {
       // Because we know the function is intercepted, we need an extra
       // parameter.
       return js.fun(['_'], js.return_(js['$functionName(this)']));
     }
 
@@ skipping 40 matching lines @@
       if (emitter.compiler.enableMinification) targetBuffer.add(';');
       targetBuffer.add(jsAst.prettyPrint(
           new jsAst.ExpressionStatement(init), compiler));
       targetBuffer.add('\n');
     }
 
     targetBuffer.add(nativeBuffer);
     targetBuffer.add('\n');
   }
 }