Add GYP build rule for Try Dart!

dart/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart

Index: dart/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart
diff --git a/dart/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart b/dart/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart
index 36596aaa2b91d4e02e92a1f87ddd0e251d239851..e639c4e52e9ef70a071500a93f9cdda7c92eff84 100644
--- a/dart/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart
+++ b/dart/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart
@@ -31,6 +31,8 @@ var handler;
 RandomAccessFile output;
 Uri outputUri;
 Uri sdkRoot;
+const bool outputJson =
+    const bool.fromEnvironment('outputJson', defaultValue: false);
 
 main(List<String> arguments) {
   handler = new FormattingDiagnosticHandler()
@@ -77,7 +79,10 @@ jsonify(MirrorSystem mirrors) {
     }
   });
 
-  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.
@@ -88,7 +93,8 @@ jsonify(MirrorSystem mirrors) {
 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();
 }