Add support for building patched_sdk and platform.dill for dart2js:

pkg/compiler/tool/generate_kernel.dart

Index: pkg/compiler/tool/generate_kernel.dart
diff --git a/pkg/compiler/tool/generate_kernel.dart b/pkg/compiler/tool/generate_kernel.dart
new file mode 100644
index 0000000000000000000000000000000000000000..cefba3b32ac5bcef53f2979bb0f01c64a7e1719f
--- /dev/null
+++ b/pkg/compiler/tool/generate_kernel.dart
@@ -0,0 +1,36 @@
+// Copyright (c) 2017, 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.
+
+/// Helper to run fasta with the right target configuration to build dart2js
+/// applications using the dart2js platform libraries.
+// TODO(sigmund): delete this file once we can configure fasta directly on the
+// command line.
+library front_end.tool.compile_dart2js;
+
+import 'dart:io' show exitCode;
+
+import 'package:front_end/src/fasta/compiler_command_line.dart'
+    show CompilerCommandLine;
+import 'package:front_end/src/fasta/compiler_context.dart' show CompilerContext;
+import 'package:front_end/src/fasta/errors.dart' show InputError;
+import 'package:front_end/src/fasta/ticker.dart' show Ticker;
+import 'package:compiler/src/kernel/fasta_support.dart' show Dart2jsCompileTask;
+
+main(List<String> arguments) async {
+  try {
+    await CompilerCommandLine.withGlobalOptions("compile_dart2js", arguments,
+        (CompilerContext c) async {
+      if (c.options.verbose) {
+        print("Compiling directly to Kernel: ${arguments.join(' ')}");
+      }
+      var task =
+          new Dart2jsCompileTask(c, new Ticker(isVerbose: c.options.verbose));
+      await task.compile();
+    });
+  } on InputError catch (e) {
+    exitCode = 1;
+    print(e.format());
+    return null;
+  }
+}