Add CrAppProtocol for headless on Mac

headless/lib/browser/headless_shell_application_mac.mm

Index: headless/lib/browser/headless_shell_application_mac.mm
diff --git a/headless/lib/browser/headless_shell_application_mac.mm b/headless/lib/browser/headless_shell_application_mac.mm
new file mode 100644
index 0000000000000000000000000000000000000000..fa8e87a9328109c83a1b8d945049af34c5a2bd61
--- /dev/null
+++ b/headless/lib/browser/headless_shell_application_mac.mm
@@ -0,0 +1,17 @@
+// 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.
+
+#include "headless/lib/browser/headless_shell_application_mac.h"
+
+#include "base/auto_reset.h"
+
+@implementation HeadlessShellCrApplication
+
+- (BOOL)isHandlingSendEvent {
+  // The CrAppProtocol must return true if [NSApplication sendEvent:] is
+  // currently on the stack. seee |CrAppProtocol| in |MessagePumpMac|.
+  return true;
+}
+
+@end