Fix try.

pkg/compiler/samples/jsonify/jsonify.dart

 // Copyright (c) 2013, 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 'dart:io';
 import 'dart:convert';
 
 import 'dart:mirrors';
 
 import 'package:_internal/libraries.dart'
@@ skipping 52 matching lines @@
       .then(jsonify);
 }
 
 jsonify(MirrorSystem mirrors) {
   var map = <String, String>{};
 
   mirrors.libraries.forEach((_, LibraryMirror library) {
     BackDoor.compilationUnitsOf(library).forEach((compilationUnit) {
       Uri uri = compilationUnit.uri;
       String filename = relativize(sdkRoot, uri, false);
-      SourceFile file = handler.provider.sourceFiles['$uri'];
+      SourceFile file = handler.provider.sourceFiles[uri];
       map['sdk:/$filename'] = file.slowText();
     });
   });
 
   LIBRARIES.forEach((name, info) {
     var patch = info.dart2jsPatchPath;
     if (patch != null) {
       Uri uri = sdkRoot.resolve('sdk/lib/$patch');
       String filename = relativize(sdkRoot, uri, false);
-      SourceFile file = handler.provider.sourceFiles['$uri'];
+      SourceFile file = handler.provider.sourceFiles[uri];
       map['sdk:/$filename'] = file.slowText();
     }
   });
 
   if (outputJson) {
     output.writeStringSync(JSON.encode(map));
   } else {
     output.writeStringSync('''
 // Copyright (c) 2013, 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.
 
 // DO NOT EDIT.
 // This file is generated by jsonify.dart.
 
 library dart.sdk_sources;
 
 const Map<String, String> SDK_SOURCES = const <String, String>''');
     output.writeStringSync(JSON.encode(map).replaceAll(r'$', r'\$'));
     output.writeStringSync(';\n');
   }
   output.closeSync();
 }