Don't send PP_Vars/V8 values with cycles across PostMessage

ppapi/api/ppb_messaging.idl

Index: ppapi/api/ppb_messaging.idl
diff --git a/ppapi/api/ppb_messaging.idl b/ppapi/api/ppb_messaging.idl
index 647f7f69e643ea656a8a94f5e05d652af8ccab2a..ce4881ab1e1a887b88c9be19f7632d89ac626c8a 100644
--- a/ppapi/api/ppb_messaging.idl
+++ b/ppapi/api/ppb_messaging.idl
@@ -36,8 +36,9 @@ interface PPB_Messaging {
    * JavaScript.
    *
    * When passing array or dictionary <code>PP_Var</code>s, the entire reference
-   * graph will be converted and transferred, including reference cycles if they
-   * exist.
+   * graph will be converted and transferred. If the reference graph has cycles,
+   * an undefined var will be sent instead and an error will be logged to the

[dmichael (off chromium), 2013/06/04 16:59:10]

Is this the behavior that was discussed in the meeting last week? I would have
assumed we would send no message to the other side (But log an error).

[raymes, 2013/06/04 19:36:06]

We discussed both and there wasn't a clear decision. I think both make sense (in
one way it's nice for an application to get notified if the var is ignored). But
I don't mind either way. I changed it to drop the var.

[dmichael (off chromium), 2013/06/05 17:05:47]

Yeah, I could see both sides. Dropping it seems less surprising to me, I guess.
I think passing a message with unexpected contents might be more likely to
result in weird/bad behavior to a user.

Hopefully the log message provides enough notification to the developer and/or
user.

+   * console.
    *
    * Listeners for message events in JavaScript code will receive an object
    * conforming to the HTML 5 <code>MessageEvent</code> interface.