Add HeadlessTabSocket

headless/lib/tab_socket.mojom

Index: headless/lib/tab_socket.mojom
diff --git a/headless/lib/tab_socket.mojom b/headless/lib/tab_socket.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..cd90e708dd363f9ba6c9e38b82b225d9dc44af23
--- /dev/null
+++ b/headless/lib/tab_socket.mojom
@@ -0,0 +1,14 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module headless;
+
+interface TabSocket {
+  // Send a message from the Tab to C++ embedder.
+  SendMessageToEmbedder(string message);
+
+  // Waits for the next message to sent from the embedder C++ to the tab.
+  // NB this is non-blocking.
+  AwaitNextMessageFromEmbedder() => (string message);
+};