C bindings pt3: Type table definitions and barebones files to get generated code to compile.

mojo/public/c/bindings/lib/type_descriptor.c

+// 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.
+
+#include "mojo/public/c/bindings/lib/type_descriptor.h"
+
+#include <stddef.h>
+
+const struct MojomTypeDescriptorArray g_mojom_string_type_description = {
+    MOJOM_TYPE_DESCRIPTOR_TYPE_POD,  // elem_descriptor
+    NULL,                            // elem_table
+    0,                               // num_elements
+    false,                           // nullable
+};