Implement the generate-kernel api by invoking dartk. Add example that uses this API to generate a by

pkg/front_end/tool/example.dart

Index: pkg/front_end/tool/example.dart
diff --git a/pkg/front_end/tool/example.dart b/pkg/front_end/tool/example.dart
new file mode 100644
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--- /dev/null
+++ b/pkg/front_end/tool/example.dart
@@ -0,0 +1,27 @@
+import 'dart:async';
+
+import 'package:front_end/kernel_generator.dart';
+import 'package:front_end/compiler_options.dart';
+import 'package:kernel/binary/ast_to_binary.dart';
+import 'package:kernel/kernel.dart' show Program;
+
+Future dumpToSink(Program program, StreamSink<List<int>> sink) {
+  new BinaryPrinter(sink).writeProgramFile(program);
+  return sink.close();
+}
+
+Future kernelToSink(Uri entry, StreamSink<List<int>> sink) async {
+  var program = await kernelForProgram(entry,
+      new CompilerOptions()
+        ..sdkPath = 'sdk'
+        ..packagesFilePath = '.packages'
+        ..onError = (e) => print(e.message));
+
+  await dumpToSink(program, sink);
+}
+
+main(args) async {
+  kernelToSink(Uri.base.resolve(args[0]),
+      // TODO(sigmund,hausner): define memory type where to dump binary data.
+      new StreamController<List<int>>.broadcast().sink);
+}