Use a test BrowserContext in DownloadItemImpl unittests.

content/browser/download/download_item_impl.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.
 
 // File method ordering: Methods in this file are in the same order as
 // in download_item_impl.h, with the following exception: The public
 // interface Start is placed in chronological order with the other
 // (private) routines that together define a DownloadItem's state
 // transitions as the download progresses.  See "Download progression
 // cascade" later in this file.
@@ skipping 1680 matching lines @@
     received_bytes_ = 0;
     hash_state_ = "";
     last_modified_time_ = "";
     etag_ = "";
   }
 
   scoped_ptr<DownloadUrlParameters> download_params;
   if (GetWebContents()) {
     download_params = DownloadUrlParameters::FromWebContents(GetWebContents(),
                                                              GetOriginalUrl());
-  } else if (GetBrowserContext()) {
+  } else {
     download_params = make_scoped_ptr(
         new DownloadUrlParameters(GetOriginalUrl(), -1, -1, -1,
                                   GetBrowserContext()->GetResourceContext()));
-  } else {
-    return;
   }
 
   download_params->set_file_path(GetFullPath());
   download_params->set_offset(GetReceivedBytes());
   download_params->set_hash_state(GetHashState());
   download_params->set_last_modified(GetLastModifiedTime());
   download_params->set_etag(GetETag());
   download_params->set_callback(
       base::Bind(&DownloadItemImpl::OnResumeRequestStarted,
                  weak_ptr_factory_.GetWeakPtr()));
@@ skipping 80 matching lines @@
     case RESUME_MODE_USER_CONTINUE:
       return "USER_CONTINUE";
     case RESUME_MODE_USER_RESTART:
       return "USER_RESTART";
   }
   NOTREACHED() << "Unknown resume mode " << mode;
   return "unknown";
 }
 
 }  // namespace content