dart2js cleanup: remove unused imports and variables

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:async';
+import 'dart:convert';
 import 'dart:io';
-import 'dart:convert';
-
 import 'dart:mirrors';
 
-import 'package:sdk_library_metadata/libraries.dart'
-    show libraries, LibraryInfo;
+import 'package:sdk_library_metadata/libraries.dart' show libraries;
 
+import '../../lib/src/filenames.dart';
 import '../../lib/src/mirrors/analyze.dart' show analyze;
 import '../../lib/src/mirrors/dart2js_mirrors.dart' show BackDoor;
-
-import '../../lib/src/filenames.dart';
 import '../../lib/src/source_file_provider.dart';
 import '../../lib/src/util/uri_extras.dart';
 
 const DART2JS = '../../lib/src/dart2js.dart';
 const DART2JS_MIRROR = '../../lib/src/mirrors/dart2js_mirror.dart';
 const SDK_ROOT = '../../../../sdk/';
 
 bool isPublicDart2jsLibrary(String name) {
   return !name.startsWith('_') && libraries[name].isDart2jsLibrary;
 }
@@ skipping 75 matching lines @@
 
 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();
   });
 }