Add the request picker and a unit test

components/offline_pages/background/request_picker.cc

+// Copyright 2016 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/offline_pages/background/request_picker.h"
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "components/offline_pages/background/save_page_request.h"
+
+namespace offline_pages {
+
+RequestPicker::RequestPicker(
+    RequestQueue* requestQueue)
+    : queue_(requestQueue),
+      weak_ptr_factory_(this) {}
+
+RequestPicker::~RequestPicker() {}
+
+void RequestPicker::ChooseNextRequest(
+    RequestCoordinator::RequestPickedCallback picked_callback,
+    RequestCoordinator::RequestQueueEmptyCallback empty_callback) {
+  picked_callback_ = picked_callback;
+  empty_callback_ = empty_callback;
+  // Get all requests from queue (there is no filtering mechanism).
+  queue_->GetRequests(base::Bind(&RequestPicker::GetRequestResultCallback,
+                                 weak_ptr_factory_.GetWeakPtr()));
+}
+
+void RequestPicker::GetRequestResultCallback(
+    RequestQueue::GetRequestsResult,
+    const std::vector<SavePageRequest>& requests) {
+  // If there is nothing to do, return right away.
+  if (requests.size() == 0) {
+    empty_callback_.Run();
+    return;
+  }
+
+  // Pick the most deserving request for our conditions.
+  const SavePageRequest& picked_request = requests[0];
+
+  // When we have a best request to try next, get the request coodinator to
+  // start it.
+  picked_callback_.Run(picked_request);
+}
+
+}  // namespace offline_pages