dart2js: move NativeEmitter into js_emitter directory.

pkg/compiler/lib/src/js_emitter/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;
+part of dart2js.js_emitter;
 
 class NativeEmitter {
 
   final Map<Element, ClassBuilder> cachedBuilders;
 
   final CodeEmitterTask emitterTask;
 
   // Whether the application contains native classes.
   bool hasNativeClasses = false;
 
@@ skipping 191 matching lines @@
         }
         String encoding = sb.toString();
 
         ClassBuilder builder = builders[classElement];
         if (builder == null) {
           // No builder because this is an intermediate mixin application or
           // Interceptor - these are not direct native classes.
           if (encoding != '') {
             Map<String, jsAst.Expression> properties =
                 additionalProperties.putIfAbsent(classElement,
-                    () => new LinkedHashMap<String, jsAst.Expression>());
+                    () => new Map<String, jsAst.Expression>());
             properties[backend.namer.nativeSpecProperty] = js.string(encoding);
           }
         } else {
           builder.addProperty(
               backend.namer.nativeSpecProperty, js.string(encoding));
         }
       }
       generateClassInfo(backend.jsInterceptorClass);
       for (ClassElement classElement in classes) {
         generateClassInfo(classElement);
@@ skipping 242 matching lines @@
         targetOutput.add(';');
       }
       targetOutput.addBuffer(jsAst.prettyPrint(
           new jsAst.ExpressionStatement(init), compiler));
       targetOutput.add('\n');
     }
 
     targetOutput.add('\n');
   }
 }