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..d50e810d2c07146bb39e6d3c45fae1fef89f9705 100644
--- a/ppapi/api/ppb_messaging.idl
+++ b/ppapi/api/ppb_messaging.idl
@@ -36,8 +36,8 @@ 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,
+   * the var will be dropped and an error will be logged to the console.

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

Might as well be crystal clear, "var will be dropped" -> "message will not be
sent". (Ditto for PPP)

We should also update the C++ documentation.

[raymes, 2013/06/05 22:48:26]

Done.

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