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

remoting/client/plugin/chromoting_scriptable_object.h

Index: remoting/client/plugin/chromoting_scriptable_object.h
diff --git a/remoting/client/plugin/chromoting_scriptable_object.h b/remoting/client/plugin/chromoting_scriptable_object.h
index 8ee2d12ff8d047e10415ed426365aa9fb05ea5c4..b0a9132b785f343cadd6044a053bed2319d7dc8b 100644
--- a/remoting/client/plugin/chromoting_scriptable_object.h
+++ b/remoting/client/plugin/chromoting_scriptable_object.h
@@ -7,6 +7,16 @@
 //
 // 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;