Add a mojoPrivate API that exposes mojo to component apps/extensions.

extensions/common/api/mojo_private.idl

+// Copyright 2015 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.
+
+// The chrome.mojoPrivate API provides access to the mojo modules.
+namespace mojoPrivate {
+
+  // |modules| is an array of the values returned by |dependencies| factories.
+  callback DefineCallback = void (any[] modules);
+
+  interface Functions {
+    // Defines a AMD module.
+    [nocompile] static void define(
+        DOMString moduleName,
+        optional DOMString[] dependencies,
+        DefineCallback factory);
+  };
+
+};