Don't do a callback when suppressing a dialog.

chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.cc

 // Copyright 2016 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.
 
 #include "chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h"
 
 #include "base/bind.h"
 #include "base/feature_list.h"
 #include "base/metrics/histogram_macros.h"
 #include "chrome/browser/engagement/site_engagement_service.h"
@@ skipping 65 matching lines @@
   if (IsEnabled()) {
     content::WebContents* parent_web_contents =
         WebContentsObserver::web_contents();
 
     if (!IsWebContentsForemost(parent_web_contents) &&
         message_type == content::JAVASCRIPT_MESSAGE_TYPE_PROMPT) {
       // Don't allow "prompt" dialogs to steal the user's focus. TODO(avi):
       // Eventually, for subsequent phases of http://bit.ly/project-oldspice,
       // turn off focus stealing for other dialog types.
       *did_suppress_message = true;
-      callback.Run(false, base::string16());
       return;
     }
 
     if (dialog_) {
       // There's already a dialog up; clear it out.
       CloseDialog(false, false, base::string16());
     }
 
     parent_web_contents->GetDelegate()->ActivateContents(parent_web_contents);
 
@@ skipping 105 matching lines @@
   DCHECK(dialog_);
 
   dialog_->CloseDialogWithoutCallback();
   if (!suppress_callback)
     dialog_callback_.Run(success, user_input);
 
   dialog_.reset();
   dialog_callback_.Reset();
   BrowserList::RemoveObserver(this);
 }