Disable the use of __proto__ in incremental mode.

pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart

 // Copyright (c) 2014, 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 dart2js.js_emitter;
 
 
 class OldEmitter implements Emitter {
   final Compiler compiler;
   final CodeEmitterTask task;
@@ skipping 1175 matching lines @@
       properties.__MAGIC_SLOW_PROPERTY = 1;
       delete properties.__MAGIC_SLOW_PROPERTY;
       return properties;
     }''');
 
     output.addBuffer(jsAst.prettyPrint(convertToSlowObject, compiler));
     output.add(N);
   }
 
   void emitSupportsDirectProtoAccess(CodeOutput output) {
-    jsAst.Statement supportsDirectProtoAccess = js.statement(r'''
-      var supportsDirectProtoAccess = (function () {
-        var cls = function () {};
-        cls.prototype = {'p': {}};
-        var object = new cls();
-        return object.__proto__ &&
-               object.__proto__.p === cls.prototype.p;
-       })();
-    ''');
+    jsAst.Statement supportsDirectProtoAccess;
+
+    if (compiler.hasIncrementalSupport) {
+      supportsDirectProtoAccess = js.statement(r'''
+        var supportsDirectProtoAccess = false;
+      ''');
+    } else {
+      supportsDirectProtoAccess = js.statement(r'''
+        var supportsDirectProtoAccess = (function () {
+          var cls = function () {};
+          cls.prototype = {'p': {}};
+          var object = new cls();
+          return object.__proto__ &&
+                 object.__proto__.p === cls.prototype.p;
+         })();
+      ''');
+    }
 
     output.addBuffer(jsAst.prettyPrint(supportsDirectProtoAccess, compiler));
     output.add(N);
   }
 
   void writeLibraryDescriptor(CodeOutput output, LibraryElement library) {
     var uri = "";
     if (!compiler.enableMinification || backend.mustPreserveUris) {
       uri = library.canonicalUri;
       if (uri.scheme == 'file' && compiler.outputUri != null) {
@@ skipping 905 matching lines @@
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {
       if (element.isInstanceMember) {
         cachedClassBuilders.remove(element.enclosingClass);
 
         nativeEmitter.cachedBuilders.remove(element.enclosingClass);
 
       }
     }
   }
 }