[Downloads] Always call DM::StartDownload() for explicit downloads.

content/browser/download/drag_download_file.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 "content/browser/download/drag_download_file.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/files/file.h"
@@ skipping 79 matching lines @@
  private:
   ~DragDownloadFileUI() override {
     DCHECK_CURRENTLY_ON(BrowserThread::UI);
     if (download_item_)
       download_item_->RemoveObserver(this);
   }
 
   void OnDownloadStarted(DownloadItem* item,
                          DownloadInterruptReason interrupt_reason) {
     DCHECK_CURRENTLY_ON(BrowserThread::UI);
-    if (!item) {
-      DCHECK_NE(DOWNLOAD_INTERRUPT_REASON_NONE, interrupt_reason);
+    if (!item || item->GetState() != DownloadItem::IN_PROGRESS) {
+      DCHECK(!item || item->GetLastReason() != DOWNLOAD_INTERRUPT_REASON_NONE);
       on_completed_loop_->task_runner()->PostTask(
           FROM_HERE, base::Bind(on_completed_, false));
       return;
     }
     DCHECK_EQ(DOWNLOAD_INTERRUPT_REASON_NONE, interrupt_reason);
     download_item_ = item;
     download_item_->AddObserver(this);
   }
 
   // DownloadItem::Observer:
@@ skipping 129 matching lines @@
 
 void DragDownloadFile::CheckThread() {
 #if defined(OS_WIN)
   DCHECK(drag_message_loop_ == base::MessageLoop::current());
 #else
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 #endif
 }
 
 }  // namespace content