Fix a crash during installing an extension with shared modules.

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 <vector>
 
 #include "base/basictypes.h"
 #include "base/bind.h"
@@ skipping 474 matching lines @@
   }
 
   if (!download_started_) {
     if (delegate_)
       delegate_->OnExtensionDownloadStarted(id_, download_item_);
     download_started_ = true;
   }
 }
 
 void WebstoreInstaller::OnDownloadUpdated(DownloadItem* download) {
-  CHECK_EQ(download_item_, download);
+  // DownloadItemImpl calls the observer for a completed item, ignore it.
+  if (download_item_ != download)
+    return;
 
   switch (download->GetState()) {
     case DownloadItem::CANCELLED:
       ReportFailure(kDownloadCanceledError, FAILURE_REASON_CANCELLED);
       break;
     case DownloadItem::INTERRUPTED:
       RecordInterrupt(download);
       ReportFailure(kDownloadInterruptedError, FAILURE_REASON_OTHER);
       break;
     case DownloadItem::COMPLETE:
@@ skipping 244 matching lines @@
         1,
         kMaxSizeKb,
         kNumBuckets);
   }
   UMA_HISTOGRAM_BOOLEAN(
       "Extensions.WebstoreDownload.InterruptTotalSizeUnknown",
       total_bytes <= 0);
 }
 
 }  // namespace extensions