Add GYP build rule for Try Dart!

dart/sdk/lib/_internal/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';
 
 // TODO(ahe): Should be dart:mirrors.
 import '../../implementation/mirrors/mirrors.dart';
 
@@ skipping 13 matching lines @@
 const SDK_ROOT = '../../../../../';
 
 bool isPublicDart2jsLibrary(String name) {
   return !name.startsWith('_') && LIBRARIES[name].isDart2jsLibrary;
 }
 
 var handler;
 RandomAccessFile output;
 Uri outputUri;
 Uri sdkRoot;
+const bool outputJson =
+    const bool.fromEnvironment('outputJson', defaultValue: false);
 
 main(List<String> arguments) {
   handler = new FormattingDiagnosticHandler()
       ..throwOnError = true;
 
   outputUri =
       handler.provider.cwd.resolve(nativeToUriPath(arguments.first));
   output = new File(arguments.first).openSync(mode: FileMode.WRITE);
 
   Uri myLocation =
@@ skipping 26 matching lines @@
   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'];
       map['sdk:/$filename'] = file.slowText();
     }
   });
 
-  output.writeStringSync('''
+  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'$', r'\$'));
-  output.writeStringSync(';\n');
+    output.writeStringSync(JSON.encode(map).replaceAll(r'$', r'\$'));
+    output.writeStringSync(';\n');
+  }
   output.closeSync();
 }