PPAPI: Disallow blocking callbacks while handling a blocking message

ppapi/c/pp_errors.h

Index: ppapi/c/pp_errors.h
diff --git a/ppapi/c/pp_errors.h b/ppapi/c/pp_errors.h
index e65bb92144b8ce7ac09bd84bcca92d3b9b26ed40..495767e8c80a4cf41a5a1dd0445efe6987b7e2da 100644
--- a/ppapi/c/pp_errors.h
+++ b/ppapi/c/pp_errors.h
@@ -3,7 +3,7 @@
  * found in the LICENSE file.
  */
 
-/* From pp_errors.idl modified Thu May 15 16:12:26 2014. */
+/* From pp_errors.idl modified Tue Sep 23 11:55:48 2014. */
 
 #ifndef PPAPI_C_PP_ERRORS_H_
 #define PPAPI_C_PP_ERRORS_H_
@@ -141,6 +141,14 @@ enum {
    */
   PP_ERROR_WRONG_THREAD = -52,
   /**
+   * Returned if you try to use a null completion callback to "block until
+   * complete" on a thread that is handling a blocking message from JavaScript.
+   * Using blocking completion callbacks while servicing a blocking JavaScript
+   * is not permitted, because doing so may block the main JavaScript thread
+   * excessively.
+   */
+  PP_ERROR_WOULD_BLOCK_THREAD = -53,
+  /**
    * This value indicates that the connection was closed. For TCP sockets, it
    * corresponds to a TCP FIN.
    */