Fix crashes when using translate in incognito by overriding some methods.

ios/web_view/internal/translate/web_view_translate_ranker_factory.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/translate/web_view_translate_ranker_factory.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "base/memory/singleton.h"
@@ skipping 35 matching lines @@
               web_view_browser_state->GetStatePath()),
           translate::TranslateRankerImpl::GetModelURL(),
           nullptr /* ukm::UkmRecorder */);
   // WebView has no consumer of translate ranker events, so don't generate them.
   ranker->EnableLogging(false);
 
   // TODO(crbug.com/703565): remove std::move() once Xcode 9.0+ is required.
   return std::move(ranker);
 }
 
+web::BrowserState* WebViewTranslateRankerFactory::GetBrowserStateToUse(
+    web::BrowserState* context) const {
+  // Override to enable this service for off the record browser states.
+  return context;
+}
+
 }  // namespace ios_web_view