Add basic versioning check to Chromoting's plugin/JS code.

remoting/client/plugin/chromoting_scriptable_object.h

 // Copyright (c) 2011 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.
 
 // This implements the JavaScript class entrypoint for the plugin instance.
 // The Javascript API is defined as follows.
 //
 // interface ChromotingScriptableObject {
 //
+//   // Chromoting session API version (for this plugin).
+//   // This is compared with the javascript API version to verify that they are
+//   // compatible.
+//   readonly attribute unsigned short apiVersion;
+//
+//   // The oldest API version that we support.
+//   // This will differ from |apiVersion| if we decide to maintain backward
+//   // compatibility with older API versions.
+//   readonly attribute unsigned short apiMinVersion;
+//
 //   // Dimension of the desktop area.
 //   readonly attribute int desktopWidth;
 //   readonly attribute int desktopHeight;
 //
 //   // Connection status.
 //   readonly attribute unsigned short status;
 //
 //   // Statistics.
 //   // Video Bandwidth in bytes per second.
 //   readonly attribute float videoBandwidth;
@@ skipping 190 matching lines @@
   PropertyNameMap property_names_;
   std::vector<PropertyDescriptor> properties_;
   scoped_refptr<PepperXmppProxy> xmpp_proxy_;
 
   ChromotingInstance* instance_;
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_CLIENT_PLUGIN_CHROMOTING_SCRIPTABLE_OBJECT_H_