Add mojom for WindowOpenDisposition

ui/base/mojo/BUILD.gn

Index: ui/base/mojo/BUILD.gn
diff --git a/ui/base/mojo/BUILD.gn b/ui/base/mojo/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..97cf16074446dbbb98ff3cc09489d10f8b20128a
--- /dev/null
+++ b/ui/base/mojo/BUILD.gn
@@ -0,0 +1,11 @@
+# Copyright 2016 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.
+
+import("//mojo/public/tools/bindings/mojom.gni")
+
+mojom("mojo_bindings") {
+  sources = [
+    "window_open_disposition.mojom",
+  ]
+}