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

ios/web_view/internal/translate/web_view_translate_service.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_TRANSLATE_WEB_VIEW_TRANSLATE_SERVICE_H_
+#define IOS_WEB_VIEW_INTERNAL_TRANSLATE_WEB_VIEW_TRANSLATE_SERVICE_H_
+
+#include "base/macros.h"
+#include "base/memory/ptr_util.h"
+#include "components/web_resource/resource_request_allowed_notifier.h"
+
+namespace base {
+template <typename T>
+struct DefaultSingletonTraits;
+}
+
+namespace ios_web_view {
+
+// Singleton managing the resources required for Translate.
+class WebViewTranslateService {
+ public:
+  static WebViewTranslateService* GetInstance();
+
+  // Must be called before the Translate feature can be used.
+  void Initialize();
+
+  // Must be called to shut down the Translate feature.
+  void Shutdown();
+
+ private:
+  // Manages enabling translate requests only when resource requests are
+  // allowed.
+  // NOTE: This currently must be a separate class from WebViewTranslateService

[sdefresne, 2017/06/01 08:36:52]

Can you create a bug to track fixing the destructor and add TODO(crbug.com/xxx)
here?

[michaeldo, 2017/06/01 21:20:38]

Done.

+  // because the destructor of
+  // web_resource::ResourceRequestAllowedNotifier::Observer is not virtual.
+  class TranslateRequestsAllowedListener
+      : public web_resource::ResourceRequestAllowedNotifier::Observer {
+   public:
+    TranslateRequestsAllowedListener();
+    ~TranslateRequestsAllowedListener();
+
+    // ResourceRequestAllowedNotifier::Observer methods.
+    void OnResourceRequestsAllowed() override;
+
+   private:
+    // Notifier class to know if it's allowed to make network resource requests.
+    web_resource::ResourceRequestAllowedNotifier
+        resource_request_allowed_notifier_;
+
+    DISALLOW_COPY_AND_ASSIGN(TranslateRequestsAllowedListener);
+  };
+
+  WebViewTranslateService();
+  ~WebViewTranslateService();
+
+  friend struct base::DefaultSingletonTraits<WebViewTranslateService>;
+
+  // Listener which manages when translate requests can occur.
+  std::unique_ptr<TranslateRequestsAllowedListener>

[sdefresne, 2017/06/01 08:36:52]

You don't need a std::unique_ptr<> here, you can just have a instance of the
correct type directly:

  TranslateRequestsAllowedListener translate_requests_allowed_listener_;

IMO, I would only use a pointer here if I want to either:
1. allow to have the pointer points to different object or allow it to be null,
2. if I want to only forward-declare the type and not include the header.

Since 2. is not true (as the type is defined a few lines before) and 1. is not
true either (as the object is constructed in WebViewTranslateService constructor
and only deallocated in the destructor), I think it is best to not use a pointer
and reduce the number of separate allocations.

[michaeldo, 2017/06/01 21:20:38]

Thank you for the explanation. Done.

+      translate_requests_allowed_listener_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebViewTranslateService);
+};
+
+}  // namespace ios_web_view
+
+#endif  // IOS_WEB_VIEW_INTERNAL_TRANSLATE_WEB_VIEW_TRANSLATE_SERVICE_H_