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..01b6dbc351db97341564184c98901ff98cc025e7 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 15:37:27 2014. */
 
 #ifndef PPAPI_C_PP_ERRORS_H_
 #define PPAPI_C_PP_ERRORS_H_
@@ -141,6 +141,13 @@ enum {
    */
   PP_ERROR_WRONG_THREAD = -52,
   /**
+   * Indicates that a null completion callback was used on a thread handling a
+   * blocking message from JavaScript. Null completion callbacks "block until
+   * complete", which could cause the main JavaScript thread to be blocked
+   * excessively.
+   */
+  PP_ERROR_WOULD_BLOCK_THREAD = -53,
+  /**
    * This value indicates that the connection was closed. For TCP sockets, it
    * corresponds to a TCP FIN.
    */