pkg/compiler: fix imports

pkg/compiler/lib/src/js_backend/constant_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.
 
 import '../common.dart';
 import '../compiler.dart' show Compiler;
 import '../constants/values.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../io/code_output.dart';
 import '../js/js.dart' as jsAst;
 import '../js/js.dart' show js;
+import 'backend.dart';
 import 'constant_system_javascript.dart';
-
-import 'backend.dart';
 import 'namer.dart';
 
 typedef jsAst.Expression _ConstantReferenceGenerator(ConstantValue constant);
 
 typedef jsAst.Expression _ConstantListGenerator(jsAst.Expression array);
 
 /**
  * Generates the JavaScript expressions for constants.
  *
  * It uses a given [constantReferenceGenerator] to reference nested constants
@@ skipping 307 matching lines @@
           [value, argumentList]);
     }
     return value;
   }
 
   @override
   jsAst.Expression visitDeferred(DeferredConstantValue constant, [_]) {
     return constantReferenceGenerator(constant.referenced);
   }
 }