Allow dartk to print out binary Kernel IR results to stdout if requested.

pkg/kernel/lib/kernel.dart

Index: pkg/kernel/lib/kernel.dart
diff --git a/pkg/kernel/lib/kernel.dart b/pkg/kernel/lib/kernel.dart
index 361f59aaa265445c0a472feb4138df8e821c00b3..752617b9d3fc2ed5ee541fd11667fa9026c92417 100644
--- a/pkg/kernel/lib/kernel.dart
+++ b/pkg/kernel/lib/kernel.dart
@@ -29,13 +29,24 @@ Program loadProgramFromBinary(String path, [Program program]) {
 }
 
 Future writeProgramToBinary(Program program, String path) {
-  var sink = new File(path).openWrite();
+  var sink;
+  if (path == 'null' || path == 'stdout') {
+    sink = stdout.nonBlocking;
+  } else {
+    sink = new File(path).openWrite();
+  }
+
   var future;
   try {
     new BinaryPrinter(sink).writeProgramFile(program);
   } finally {
-    future = sink.close();
+    if (sink == stdout.nonBlocking) {
+      future = sink.flush();
+    } else {
+      future = sink.close();
+    }
   }
+
   return future;
 }