Move common functionality of IOSChromeIOThread to ios/components.

ios/components/io_thread/io_thread_unittest.mm

+// Copyright 2017 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 "ios/components/io_thread/io_thread.h"
+
+#include "base/message_loop/message_loop.h"
+#include "base/run_loop.h"
+#include "components/prefs/pref_registry_simple.h"
+#include "components/prefs/pref_service.h"
+#include "components/prefs/pref_service_factory.h"
+#include "components/prefs/testing_pref_store.h"
+#include "components/proxy_config/pref_proxy_config_tracker_impl.h"
+#include "components/ssl_config/ssl_config_service_manager.h"
+#include "ios/web/public/test/test_web_thread.h"
+#include "net/base/network_delegate_impl.h"
+#include "net/test/url_request/url_request_failed_job.h"
+#include "net/url_request/url_request_filter.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "testing/gtest_mac.h"
+#include "testing/platform_test.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace {
+
+// A concrete implementation of IOThread for testing.
+class TestIOThread : public io_thread::IOThread {
+ public:
+  TestIOThread(PrefService* local_state, net_log::ChromeNetLog* net_log)
+      : IOThread(local_state, net_log) {}
+  ~TestIOThread() override {}
+
+  // Dummy implementations of virtual methods.
+  std::unique_ptr<net::NetworkDelegate> GetSystemNetworkDelegate() override {
+    return base::MakeUnique<net::NetworkDelegateImpl>();
+  }
+};
+
+}  // namespace
+
+class IOThreadTest : public PlatformTest {
+ public:
+  IOThreadTest()
+      : loop_(base::MessageLoop::TYPE_IO),
+        ui_thread_(web::WebThread::UI, &loop_),
+        io_thread_(web::WebThread::IO, &loop_) {
+    net::URLRequestFailedJob::AddUrlHandler();
+  }
+
+  ~IOThreadTest() override {
+    net::URLRequestFilter::GetInstance()->ClearHandlers();
+  }
+
+ private:
+  base::MessageLoop loop_;
+  web::TestWebThread ui_thread_;
+  web::TestWebThread io_thread_;
+};
+
+TEST_F(IOThreadTest, AssertSystemUrlRequestContext) {

[Eugene But (OOO till 7-30), 2017/05/25 22:05:22]

Please add comments describing what is tested here.

[michaeldo, 2017/05/26 07:24:44]

Done.

+  PrefServiceFactory pref_service_factory;
+  pref_service_factory.set_user_prefs(
+      make_scoped_refptr(new TestingPrefStore()));
+
+  scoped_refptr<PrefRegistrySimple> pref_registry = new PrefRegistrySimple;
+  PrefProxyConfigTrackerImpl::RegisterPrefs(pref_registry.get());
+  ssl_config::SSLConfigServiceManager::RegisterPrefs(pref_registry.get());
+
+  std::unique_ptr<PrefService> pref_service(
+      pref_service_factory.Create(pref_registry.get()));
+
+  std::unique_ptr<TestIOThread> test_io_thread(
+      new TestIOThread(pref_service.get(), nullptr));
+
+  ASSERT_TRUE(test_io_thread->system_url_request_context_getter());
+}