PPAPI: Implement synchronous 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 dc50788e26db2c0fbfbd9824e260c4ae76f5a8d2..a070ddd2fe00df6d830c3a3c6e604a9ce72eaa40 100644
--- a/ppapi/api/ppb_messaging.idl
+++ b/ppapi/api/ppb_messaging.idl
@@ -86,9 +86,6 @@ interface PPB_Messaging {
   void PostMessage([in] PP_Instance instance, [in] PP_Var message);
 
   /**
-   * <strong>Note:</strong> This function is not yet implemented. Please use
-   * PPB_Messaging_1_0.
-   *
    * Registers a handler for receiving messages from JavaScript. If a handler
    * is registered this way, it will replace PPP_Messaging, and all messages
    * sent from JavaScript via postMessage and postMessageAndAwaitResponse will
@@ -123,9 +120,6 @@ interface PPB_Messaging {
                                  [in] PPP_MessageHandler handler,
                                  [in] PP_Resource message_loop);
   /**
-   * <strong>Note:</strong> This function is not yet implemented. Please use
-   * PPB_Messaging_1_0.
-   *
    * Unregisters the current message handler for <code>instance</code> if one
    * is registered. After this call, the message handler (if one was
    * registered) will have "Destroy" called on it and will receive no further