[Offline pages] Introduces TaskQueue to serialize tasks that asynchronously access SQLStore

components/offline_pages/core/test_task.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/core/test_task.h"
+
+#include "base/bind.h"
+
+namespace offline_pages {
+
+ConsumedResource::ConsumedResource() {}
+
+ConsumedResource::~ConsumedResource() {}
+
+void ConsumedResource::Step(const base::Closure& step_callback) {
+  next_step_ = step_callback;
+}
+
+void ConsumedResource::CompleteStep() {
+  base::Closure temp_ = next_step_;
+  next_step_.Reset();
+  temp_.Run();
+}
+
+TestTask::TestTask(ConsumedResource* resource)
+    : resource_(resource),
+      state_(TaskState::NOT_STARTED),
+      leave_early_(false) {}
+
+TestTask::TestTask(ConsumedResource* resource, bool leave_early)
+    : resource_(resource),
+      state_(TaskState::NOT_STARTED),
+      leave_early_(leave_early) {}
+
+TestTask::~TestTask() {}
+
+// Run is Step 1 in our case.
+void TestTask::Run() {
+  state_ = TaskState::STEP_1;
+  resource_->Step(base::Bind(&TestTask::Step2, base::Unretained(this)));
+}
+
+void TestTask::Step2() {
+  if (leave_early_) {
+    LastStep();
+    return;
+  }
+  state_ = TaskState::STEP_2;
+  resource_->Step(base::Bind(&TestTask::LastStep, base::Unretained(this)));
+}
+
+// This is step 3, but we conclude here.
+void TestTask::LastStep() {
+  state_ = TaskState::COMPLETED;
+  TaskComplete();
+}
+
+}  // namespace offline_pages