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

chrome/browser/extensions/webstore_installer.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/webstore_installer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <limits>
 #include <set>
@@ skipping 441 matching lines @@
   if (download_item_) {
     download_item_->RemoveObserver(this);
     download_item_ = NULL;
   }
 }
 
 void WebstoreInstaller::OnDownloadStarted(
     const std::string& extension_id,
     DownloadItem* item,
     content::DownloadInterruptReason interrupt_reason) {
-  if (!item) {
-    DCHECK_NE(content::DOWNLOAD_INTERRUPT_REASON_NONE, interrupt_reason);
+  if (!item || interrupt_reason != content::DOWNLOAD_INTERRUPT_REASON_NONE) {
+    if (item)
+      item->Remove();
     ReportFailure(content::DownloadInterruptReasonToString(interrupt_reason),
                   FAILURE_REASON_OTHER);
     return;
   }
 
   bool found = false;
   for (const auto& module : pending_modules_) {
     if (extension_id == module.extension_id) {
       found = true;
       break;
@@ skipping 317 matching lines @@
         1,
         kMaxSizeKb,
         kNumBuckets);
   }
   UMA_HISTOGRAM_BOOLEAN(
       "Extensions.WebstoreDownload.InterruptTotalSizeUnknown",
       total_bytes <= 0);
 }
 
 }  // namespace extensions