Pepper: Make pending_sync_msgs_ local to IO thread.

ppapi/proxy/nacl_message_scanner.h

Index: ppapi/proxy/nacl_message_scanner.h
diff --git a/ppapi/proxy/nacl_message_scanner.h b/ppapi/proxy/nacl_message_scanner.h
index d1360b72519730b4a45850fc86d9db24d9c2e202..dade0d7bbc294f1bcfcd8ee72decf492218300d0 100644
--- a/ppapi/proxy/nacl_message_scanner.h
+++ b/ppapi/proxy/nacl_message_scanner.h
@@ -39,6 +39,7 @@ class PPAPI_PROXY_EXPORT NaClMessageScanner {
   // See chrome/nacl/nacl_ipc_adapter.cc for where this is used to help convert
   // native handles to NaClDescs.
   bool ScanMessage(const IPC::Message& msg,
+                   uint32_t type,
                    std::vector<SerializedHandle>* handles,
                    scoped_ptr<IPC::Message>* new_msg_ptr);
 
@@ -99,18 +100,10 @@ class PPAPI_PROXY_EXPORT NaClMessageScanner {
 
  private:
   friend class NaClMessageScannerTest;
-
-  void RegisterSyncMessageForReply(const IPC::Message& msg);
   void AuditNestedMessage(PP_Resource resource,
                           const IPC::Message& msg,
                           SerializedHandle* handle);
 
-  // When we send a synchronous message (from untrusted to trusted), we store
-  // its type here, so that later we can associate the reply with its type
-  // for scanning.
-  typedef std::map<int, uint32> PendingSyncMsgMap;
-  PendingSyncMsgMap pending_sync_msgs_;
-
   // We intercept FileSystem and FileIO messages to maintain information about
   // file systems and open files. This is used by NaClQuotaDescs to calculate
   // quota consumption and check it against the reserved amount.