Created an interface for DownloadFile, for use in unit tests.

content/browser/download/mock_download_file.cc

+// Copyright (c) 2011 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/mock_download_file.h"
+
+MockDownloadFile::MockDownloadFile(
+    const DownloadCreateInfo* info,
+    const DownloadRequestHandle& request_handle,
+    DownloadManager* download_manager)
+        : id_(1),
+          request_handle_(request_handle),
+          download_manager_(download_manager) {
+}
+
+MockDownloadFile::~MockDownloadFile() {
+}
+
+net::Error MockDownloadFile::Initialize(bool calculate_hash) {
+  return net::OK;
+}
+
+net::Error MockDownloadFile::AppendDataToFile(
+    const char* data, size_t data_len) {
+  return net::OK;
+}
+
+net::Error MockDownloadFile::Rename(const FilePath& full_path) {
+  return net::OK;
+}
+
+void MockDownloadFile::Detach() {
+}
+
+void MockDownloadFile::Cancel() {
+}
+
+void MockDownloadFile::Finish() {
+}
+
+void MockDownloadFile::AnnotateWithSourceInformation() {
+}
+
+FilePath MockDownloadFile::FullPath() const {
+  return FilePath();
+}
+
+bool MockDownloadFile::InProgress() const {
+  return true;
+}
+
+int64 MockDownloadFile::BytesSoFar() const {
+  return 0;
+}
+
+bool GetSha256Hash(std::string* hash) {
+  return false;
+}
+
+// DownloadFileInterface implementation.
+void MockDownloadFile::CancelDownloadRequest() {
+}
+
+int MockDownloadFile::Id() const {
+  return id_;
+}
+
+DownloadManager* MockDownloadFile::GetDownloadManager() {
+  return NULL;
+}
+
+std::string MockDownloadFile::DebugString() const {
+  return "";
+}