[Extensions] DCHECK that ExtensionFunctions respond (and only once)

chrome/browser/extensions/api/downloads/downloads_api.cc

 // Copyright (c) 2012 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/extensions/api/downloads/downloads_api.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <memory>
 #include <set>
@@ skipping 1253 matching lines @@
   bool visible = platform_util::IsVisible(web_contents->GetNativeView());
   if (!visible) {
     if (retries > 0) {
       base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
           FROM_HERE, base::Bind(&DownloadsAcceptDangerFunction::PromptOrWait,
                                 this, download_id, retries - 1),
           base::TimeDelta::FromMilliseconds(100));
       return;
     }
     error_ = errors::kInvisibleContext;
-    SendResponse(error_.empty());
+    SendResponse(false);
     return;
   }
   RecordApiFunctions(DOWNLOADS_FUNCTION_ACCEPT_DANGER);
   // DownloadDangerPrompt displays a modal dialog using native widgets that the
   // user must either accept or cancel. It cannot be scripted.
   DownloadDangerPrompt* prompt = DownloadDangerPrompt::Create(
       download_item,
       web_contents,
       true,
       base::Bind(&DownloadsAcceptDangerFunction::DangerPromptCallback,
                  this, download_id));
   // DownloadDangerPrompt deletes itself
   if (on_prompt_created_ && !on_prompt_created_->is_null())
     on_prompt_created_->Run(prompt);
-  SendResponse(error_.empty());
+  // Function finishes in DangerPromptCallback().
 }
 
 void DownloadsAcceptDangerFunction::DangerPromptCallback(
     int download_id, DownloadDangerPrompt::Action action) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   DownloadItem* download_item =
       GetDownload(GetProfile(), include_incognito(), download_id);
   if (InvalidId(download_item, &error_) ||
       Fault(download_item->GetState() != DownloadItem::IN_PROGRESS,
             errors::kNotInProgress, &error_))
@@ skipping 603 matching lines @@
     return;
   base::Time now(base::Time::Now());
   int delta = now.ToTimeT() - last_checked_removal_.ToTimeT();
   if (delta <= kFileExistenceRateLimitSeconds)
     return;
   last_checked_removal_ = now;
   manager->CheckForHistoryFilesRemoval();
 }
 
 }  // namespace extensions