Add --analyze-signatures-only option to dart2js

sdk/lib/_internal/compiler/implementation/mirrors/dart2js_mirror.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.
 
 library mirrors_dart2js;
 
 import 'dart:async';
 import 'dart:collection' show LinkedHashMap;
 import 'dart:io';
 import 'dart:uri';
@@ skipping 262 matching lines @@
         provider = new SourceFileProvider() {
     var libraryUri = cwd.resolve('${libraryRoot}/');
     var packageUri;
     if (packageRoot != null) {
       packageUri = cwd.resolve('${packageRoot}/');
     } else {
       packageUri = libraryUri;
     }
     opts = new List<String>.from(opts);
     opts.add('--analyze-only');
+    opts.add('--analyze-signatures-only');
     opts.add('--analyze-all');
     _compiler = new Compiler(provider.readStringFromUri,
                                  null,
                                  silentDiagnosticHandler,
                                  libraryUri, packageUri, opts);
     var librariesUri = <Uri>[];
     for (Path library in libraries) {
       librariesUri.add(cwd.resolve(library.toString()));
       // TODO(johnniwinther): Detect file not found
     }
@@ skipping 1440 matching lines @@
       return new Future.immediate(
           new Dart2JsStringConstantMirror.fromString(mirrors, text));
     } else if (fieldName == 'trimmedText') {
       return new Future.immediate(
           new Dart2JsStringConstantMirror.fromString(mirrors, trimmedText));
     }
     // TODO(johnniwinther): Which exception/error should be thrown here?
     throw new UnsupportedError('InstanceMirror does not have a reflectee');
   }
 }