Use the user's preferred downloads directory for creating the initial download file.

content/browser/download/base_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/base_file.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/format_macros.h"
 #include "base/logging.h"
@@ skipping 227 matching lines @@
 }
 
 BaseFile::~BaseFile() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   if (detached_)
     Close();
   else
     Cancel();  // Will delete the file.
 }
 
-net::Error BaseFile::Initialize() {
+net::Error BaseFile::Initialize(const FilePath& default_directory) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   DCHECK(!detached_);
 
   if (full_path_.empty()) {
+    FilePath initial_directory(default_directory);
     FilePath temp_file;
-    FilePath download_dir =
-        content::GetContentClient()->browser()->GetDefaultDownloadDirectory();
-    if (!file_util::CreateTemporaryFileInDir(download_dir, &temp_file) &&
+    if (initial_directory.empty()) {
+      initial_directory =
+          content::GetContentClient()->browser()->GetDefaultDownloadDirectory();
+    }
+    // |initial_directory| can still be empty if ContentBrowserClient returned
+    // an empty path for the downloads directory.
+    if ((initial_directory.empty() ||
+         !file_util::CreateTemporaryFileInDir(initial_directory, &temp_file)) &&
         !file_util::CreateTemporaryFile(&temp_file)) {
       return LOG_ERROR("unable to create", net::ERR_FILE_NOT_FOUND);
     }
     full_path_ = temp_file;
   }
 
   return Open();
 }
 
 net::Error BaseFile::AppendDataToFile(const char* data, size_t data_len) {
@@ skipping 283 matching lines @@
 int64 BaseFile::CurrentSpeedAtTime(base::TimeTicks current_time) const {
   base::TimeDelta diff = current_time - start_tick_;
   int64 diff_ms = diff.InMilliseconds();
   return diff_ms == 0 ? 0 : bytes_so_far() * 1000 / diff_ms;
 }
 
 int64 BaseFile::CurrentSpeed() const {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   return CurrentSpeedAtTime(base::TimeTicks::Now());
 }
-