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

ios/web_view/internal/app/application_context.cc

+// 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/web_view/internal/app/application_context.h"
+
+namespace {
+// Global ApplicationContext instance.
+ApplicationContext* g_application_context = nullptr;
+}
+
+ApplicationContext* GetApplicationContext() {
+  return g_application_context;
+}
+
+ApplicationContext::ApplicationContext() {}
+
+ApplicationContext::~ApplicationContext() {}
+
+// static
+void ApplicationContext::SetApplicationContext(ApplicationContext* context) {
+  g_application_context = context;
+}