Implement support for fallback update check urls in the component updater

components/component_updater/request_sender.cc

+// Copyright 2014 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 "components/component_updater/request_sender.h"
+
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/sequenced_task_runner.h"
+#include "components/component_updater/component_updater_configurator.h"
+#include "components/component_updater/component_updater_utils.h"
+
+namespace component_updater {
+
+RequestSender::RequestSender(const Configurator& config,
+                             const std::vector<GURL>& urls)
+    : config_(config), urls_(urls) {
+}
+
+void RequestSender::Send(const std::string& request_string,
+                         const RequestSenderCallback& request_sender_callback) {
+  if (urls_.empty()) {
+    request_sender_callback.Run(NULL);
+    return;
+  }
+
+  request_sender_callback_ = request_sender_callback;
+  request_string_ = request_string;
+
+  cur_url_ = urls_.begin();
+
+  SendInternal();
+}
+
+void RequestSender::SendInternal() {
+  DCHECK(cur_url_ != urls_.end());
+  DCHECK(cur_url_->is_valid());
+
+  url_fetcher_.reset(SendProtocolRequest(
+      *cur_url_, request_string_, this, config_.RequestContext()));
+}
+
+void RequestSender::OnURLFetchComplete(const net::URLFetcher* source) {

[waffles, 2014/09/12 22:38:26]

What thread does this occur on? Is it OK to .Run the callback here, or should we
PostTask it to config_.GetSequencedTaskRunner()?

[Sorin Jianu, 2014/09/12 23:24:00]

The fetcher is thread safe, the call will occur on the thread the fetcher is
running on. We can add thread checkers or rely on the checkers in the classes
dependent on this class.

+  if (GetFetchError(*source) == 0) {
+    request_sender_callback_.Run(source);
+    return;
+  }
+
+  if (++cur_url_ != urls_.end() &&
+      config_.GetSequencedTaskRunner()->PostTask(
+          FROM_HERE,
+          base::Bind(&RequestSender::SendInternal, base::Unretained(this)))) {
+    return;
+  }
+
+  request_sender_callback_.Run(source);
+}
+
+}  // namespace component_updater