Use IPC to wait for download in DownloadTest.

chrome/test/automation/automation_messages_internal.h

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Defines the IPC messages used by the automation interface.
 
 // This header is meant to be included in multiple passes, hence no traditional
 // header guard.
 // See ipc_message_macros.h for explanation of the macros and passes.
 
@@ skipping 1378 matching lines @@
                              WindowOpenDisposition,
                              bool /* result */)
 
 
   // This message requests the cookie be delete for given url in the
   // profile of the tab identified by the first parameter.  The second
   // parameter is the cookie name.
   IPC_SYNC_MESSAGE_ROUTED3_1(AutomationMsg_DeleteCookie, GURL, std::string,
                              int, bool)
 
+  // Waits for the download shelf to appear or disappear (depending on
+  // |visibility|) and sets |success| to true on success.
+  IPC_SYNC_MESSAGE_ROUTED2_1(AutomationMsg_WaitForDownloadShelfVisibilityChange,
+                             int /* browser handle */,
+                             bool /* visibility */,
+                             bool /* success */)
+
 IPC_END_MESSAGES(Automation)