dart2js: Add a header to the output of the startup emitter.

pkg/compiler/lib/src/js_emitter/full_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.
 
 library dart2js.js_emitter.full_emitter;
 
 import 'dart:convert';
 import 'dart:collection' show HashMap;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
 import 'package:js_runtime/shared/embedded_names.dart' show
     JsBuiltin,
     JsGetName;
 
+import '../headers.dart';
+
 import '../js_emitter.dart' hide Emitter;
 import '../js_emitter.dart' as js_emitter show Emitter;
 
 import '../model.dart';
 import '../program_builder/program_builder.dart';
 
 import '../../common.dart';
 
 import '../../constants/values.dart';
 
@@ skipping 2040 matching lines @@
       } else {
         output.close();
       }
 
       hunkHashes[outputUnit] = hash;
     }
     return hunkHashes;
   }
 
   jsAst.Comment buildGeneratedBy() {
-    String suffix = '';
-    if (compiler.hasBuildId) suffix = ' version: ${compiler.buildId}';
-    String msg = '// Generated by dart2js, the Dart to JavaScript '
-                 'compiler$suffix.';
-    return new jsAst.Comment(msg);
+    return new jsAst.Comment(generatedBy(compiler));
   }
 
   void outputSourceMap(CodeOutput output,
                        LineColumnProvider lineColumnProvider,
                        String name,
                        [Uri sourceMapUri,
                         Uri fileUri]) {
     if (!generateSourceMap) return;
     // Create a source file for the compilation output. This allows using
     // [:getLine:] to transform offsets to line numbers in [SourceMapBuilder].
@@ skipping 24 matching lines @@
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {
       if (element.isInstanceMember) {
         cachedClassBuilders.remove(element.enclosingClass);
 
         nativeEmitter.cachedBuilders.remove(element.enclosingClass);
 
       }
     }
   }
 }