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 <string>
+
+#include "base/macros.h"
+
+namespace net {
+class URLRequestContextGetter;
+}
+
+namespace net_log {
+class ChromeNetLog;
+}
+
+class ApplicationContext;
+class PrefService;
+class WebViewIOThread;
+
+// Gets the global application context. Cannot return null.
+ApplicationContext* GetApplicationContext();

[Eugene But (OOO till 7-30), 2017/05/18 23:54:54]

Should this be a singleton from base/memory/singleton.h?

[michaeldo, 2017/05/19 22:02:35]

This is not a singleton in chrome/browser/io_thread.h or
ios/chrome/browser/ios_chrome_io_thread.h.

I think it is not a singleton of that form because it can't be created
automatically on first call because of the two required parameters (command_line
and locale). The "singleton" getter is actually initialized when an instance of
the object is created. PTAL at SetApplicationContext(this) inside
application_context_impl.cc. This seems like a very odd pattern and I'll look to
see if I can do something else. Maybe those required properties could be set
statically on ApplicationContextImpl then the standard singleton pattern could
be used? However, that may go against style guide restrictions on global vars.

Note I've added a note about this inside application_context_impl.h as part of
the class comment.

[Eugene But (OOO till 7-30), 2017/05/19 23:32:05]

If this interface should not be singleton, then maybe GetApplicationContext and
SetApplicationContext should not be a part of it? As it stands it looks like a
singleton, but does not use base/memory/singleton.

[michaeldo, 2017/05/23 22:38:36]

I took another look at this and was able to make it a real singleton!!! PTAL

+
+class ApplicationContext {

[Eugene But (OOO till 7-30), 2017/05/18 23:54:54]

Please add comments

[Hiroshi Ichikawa, 2017/05/19 02:37:51]

Shouldn't this class be inside a namespace?

[michaeldo, 2017/05/19 22:02:35]

I think so? While many other classes are namespaced, the ApplicationContext is
not namespaced on other platforms. However, I can add the namespace and
everything still seems ok, so yes I think the namespace is better to have unless
anyone knows why it should be excluded.

[michaeldo, 2017/05/19 22:02:35]

Done.

+ public:
+  ApplicationContext();

[Eugene But (OOO till 7-30), 2017/05/18 23:54:54]

Should constructor/destructor be protected?

[michaeldo, 2017/05/19 22:02:35]

Makes sense, Done.

+  virtual ~ApplicationContext();
+
+  // Gets the local state associated with this application.
+  virtual PrefService* GetLocalState() = 0;
+
+  // Gets the URL request context associated with this application.
+  virtual net::URLRequestContextGetter* GetSystemURLRequestContext() = 0;
+
+  // Gets the locale used by the application.
+  virtual const std::string& GetApplicationLocale() = 0;
+
+ protected:
+  // Sets the global ApplicationContext instance.
+  static void SetApplicationContext(ApplicationContext* context);
+
+  // Gets the ChromeNetLog.
+  virtual net_log::ChromeNetLog* GetNetLog() = 0;
+
+  // Gets the WebViewIOThread.
+  virtual WebViewIOThread* GetWebViewIOThread() = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ApplicationContext);
+};
+
+#endif  // IOS_WEB_VIEW_INTERNAL_APP_APPLICATION_CONTEXT_H_