Break up common_custom_types.mojom.

mojo/common/unguessable_token.typemap

Index: mojo/common/unguessable_token.typemap
diff --git a/mojo/common/unguessable_token.typemap b/mojo/common/unguessable_token.typemap
new file mode 100644
index 0000000000000000000000000000000000000000..ec7b1942b34540e16456ee11924717d4548c6b58
--- /dev/null
+++ b/mojo/common/unguessable_token.typemap
@@ -0,0 +1,12 @@
+# 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.
+
+mojom = "//mojo/common/unguessable_token.mojom"
+public_headers = [ "//base/unguessable_token.h" ]
+traits_headers = [ "//mojo/common/common_custom_types_struct_traits.h" ]
+public_deps = [
+  "//mojo/common:struct_traits",
+]
+
+type_mappings = [ "mojo.common.mojom.UnguessableToken=base::UnguessableToken" ]