enable --dump-info with the --fast-startup emitter

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 '../../deferred_load.dart' show OutputUnit;
 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 '../../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';
@@ skipping 165 matching lines @@
         return js.js.expressionTemplateFor("$functionAccess(#)");
 
       default:
         reporter.internalError(
             NO_LOCATION_SPANNABLE, "Unhandled Builtin: $builtin");
         return null;
     }
   }
 
   @override
+  int generatedSize(OutputUnit unit) {
+    Fragment key = _emitter.outputBuffers.keys
+        .firstWhere((Fragment fragment) => fragment.outputUnit == unit);
+    return _emitter.outputBuffers[key].length;
+  }
+
+  @override
   void invalidateCaches() {}
 }