Create Namer and Emitter on codegen start.

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

 // Copyright (c) 2015, 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.
 
 library dart2js.js_emitter.startup_emitter;
 
 import 'package:js_runtime/shared/embedded_names.dart'
     show JsBuiltin, METADATA, STATIC_FUNCTION_NAME_TO_CLOSURE, TYPES;
 
 import '../../common.dart';
 import '../../compiler.dart' show Compiler;
 import '../../constants/values.dart' show ConstantValue;
 import '../../elements/elements.dart'
     show ClassElement, Element, FieldElement, FunctionElement;
 import '../../js/js.dart' as js;
 import '../../js_backend/js_backend.dart' show JavaScriptBackend, Namer;
-import '../js_emitter.dart' show NativeEmitter;
-import '../js_emitter.dart' as emitterTask show Emitter;
+import '../../world.dart' show ClosedWorld;
+import '../js_emitter.dart' show CodeEmitterTask, NativeEmitter;
+import '../js_emitter.dart' as emitterTask show Emitter, EmitterFactory;
 import '../model.dart';
 import '../program_builder/program_builder.dart' show ProgramBuilder;
 import 'model_emitter.dart';
 
+class EmitterFactory implements emitterTask.EmitterFactory {
+  final bool generateSourceMap;
+
+  EmitterFactory({this.generateSourceMap});
+
+  @override
+  String get patchVersion => "startup";
+
+  @override
+  bool get supportsReflection => false;
+
+  @override
+  Emitter createEmitter(
+      CodeEmitterTask task, Namer namer, ClosedWorld closedWorld) {
+    return new Emitter(
+        task.compiler, namer, task.nativeEmitter, generateSourceMap);
+  }
+}
+
 class Emitter implements emitterTask.Emitter {
   final Compiler _compiler;
   final Namer namer;
   final ModelEmitter _emitter;
 
   JavaScriptBackend get _backend => _compiler.backend;
 
   Emitter(Compiler compiler, Namer namer, NativeEmitter nativeEmitter,
       bool shouldGenerateSourceMap)
       : this._compiler = compiler,
         this.namer = namer,
         _emitter = new ModelEmitter(
             compiler, namer, nativeEmitter, shouldGenerateSourceMap);
 
   DiagnosticReporter get reporter => _compiler.reporter;
 
   @override
-  String get patchVersion => "startup";
-
-  @override
   int emitProgram(ProgramBuilder programBuilder) {
     Program program = programBuilder.buildProgram();
     return _emitter.emitProgram(program);
   }
 
   @override
-  bool get supportsReflection => false;
-
-  @override
   bool isConstantInlinedOrAlreadyEmitted(ConstantValue constant) {
     return _emitter.isConstantInlinedOrAlreadyEmitted(constant);
   }
 
   @override
   int compareConstants(ConstantValue a, ConstantValue b) {
     return _emitter.compareConstants(a, b);
   }
 
   @override
@@ skipping 114 matching lines @@
       default:
         reporter.internalError(
             NO_LOCATION_SPANNABLE, "Unhandled Builtin: $builtin");
         return null;
     }
   }
 
   @override
   void invalidateCaches() {}
 }