Initialize ios/web_view translate with a system-wide URLRequestContext.

ios/web_view/internal/app/application_context.h

+// 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.
+
+#ifndef IOS_WEB_VIEW_INTERNAL_APP_APPLICATION_CONTEXT_H_
+#define IOS_WEB_VIEW_INTERNAL_APP_APPLICATION_CONTEXT_H_
+
+#include <memory>
+#include <string>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/threading/thread_checker.h"
+
+namespace base {
+template <typename T>
+struct DefaultSingletonTraits;
+class FilePath;
+class SequencedTaskRunner;
+}
+
+namespace net {
+class URLRequestContextGetter;
+}
+
+namespace net_log {
+class ChromeNetLog;
+}
+
+class PrefService;
+
+namespace ios_web_view {
+
+class WebViewIOThread;
+
+// Exposes application global state objects.
+class ApplicationContext {
+ public:
+  static ApplicationContext* GetInstance();
+
+  // Gets the preferences associated with this application.
+  PrefService* GetLocalState();
+
+  // Gets the URL request context associated with this application.
+  net::URLRequestContextGetter* GetSystemURLRequestContext();
+
+  // Gets the locale used by the application.
+  const std::string& GetApplicationLocale();
+
+  // Creates state tied to application threads. It is expected this will be
+  // called from web::WebMainParts::PreCreateThreads.
+  void PreCreateThreads();
+
+  // Saves applicaiton context state if |local_state_| exists. This should be

[sdefresne, 2017/06/02 09:03:51]

applicaiton → application

[michaeldo, 2017/06/02 15:46:57]

Done.

+  // called during shutdown to save application state.
+  void SaveState();
+
+  // Destroys state tied to application threads. It is expected this will be
+  // called from web::WebMainParts::PostDestroyThreads.
+  void PostDestroyThreads();
+
+ private:
+  ApplicationContext();

[sdefresne, 2017/06/02 09:03:51]

nit: move this below "friend struct
base::DefaultSingletonTraits<ApplicationContext>;" as the style guide recommends
in a given section to "group[ing] similar kinds of declarations together" and
here you are mixing "friend" and "methods".

https://google.github.io/styleguide/cppguide.html#Declaration_Order

So, this could be:

 private:
  friend struct base::DefaultSingletonTraits<ApplicationContext>;

  ApplicationContext();
  ~ApplicationContext();

  // Gets the ChromeNetLog.
  net_log::ChromeNetLog* GetNetLog();

[michaeldo, 2017/06/02 15:46:57]

Done. Thank you for reference.

+  ~ApplicationContext();
+  friend struct base::DefaultSingletonTraits<ApplicationContext>;
+
+  // Gets the ChromeNetLog.
+  net_log::ChromeNetLog* GetNetLog();
+
+  // Gets the WebViewIOThread.
+  WebViewIOThread* GetWebViewIOThread();
+
+  // Returns the path to the application level preferences.
+  static base::FilePath GetLocalStatePath();
+
+  // Sets the locale used by the application.
+  void SetApplicationLocale(const std::string& locale);
+
+  THREAD_CHECKER(thread_checker_);

[sdefresne, 2017/06/02 09:03:51]

optional: I think you can use a SEQUENCE_CHECKER here. The instance does not
uses thread-local storage and is created before any threads are started so they
should give the same result, and SEQUENCE_CHECKER is recommended.

[michaeldo, 2017/06/02 15:46:57]

Done.

+  std::unique_ptr<PrefService> local_state_;
+  std::unique_ptr<net_log::ChromeNetLog> net_log_;
+  std::unique_ptr<WebViewIOThread> web_view_io_thread_;
+  std::string application_locale_;
+
+  // Sequenced task runner for local state related I/O tasks.
+  const scoped_refptr<base::SequencedTaskRunner> local_state_task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(ApplicationContext);
+};
+
+}  // namespace ios_web_view
+
+#endif  // IOS_WEB_VIEW_INTERNAL_APP_APPLICATION_CONTEXT_H_