[translate] Fix shutdown race for translate ranker model loader.

components/translate/core/browser/translate_download_manager.h

 // Copyright 2014 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 COMPONENTS_TRANSLATE_CORE_BROWSER_TRANSLATE_DOWNLOAD_MANAGER_H_
 #define COMPONENTS_TRANSLATE_CORE_BROWSER_TRANSLATE_DOWNLOAD_MANAGER_H_
 
 #include <memory>
 #include <string>
 
 #include "base/memory/ref_counted.h"
+#include "base/sequence_checker.h"
 #include "components/translate/core/browser/translate_language_list.h"
 #include "components/translate/core/browser/translate_script.h"
 #include "net/url_request/url_request_context_getter.h"
 
 namespace base {
 template <typename T> struct DefaultSingletonTraits;
 }
 
 class PrefService;
 
 namespace translate {
 
 // Manages the downloaded resources for Translate, such as the translate script
 // and the language list.
 class TranslateDownloadManager {
  public:
   // Returns the singleton instance.
   static TranslateDownloadManager* GetInstance();
 
   // The request context used to download the resources.
   // Should be set before this class can be used.
   net::URLRequestContextGetter* request_context() {
+    DCHECK(sequence_checker_.CalledOnValidSequence());
     return request_context_.get();
   }
   void set_request_context(net::URLRequestContextGetter* context) {
-      request_context_ = context;
+    DCHECK(sequence_checker_.CalledOnValidSequence());
+    request_context_ = context;
   }
 
   // The application locale.
   // Should be set before this class can be used.
-  const std::string& application_locale() { return application_locale_; }
+  const std::string& application_locale() {
+    DCHECK(sequence_checker_.CalledOnValidSequence());
+    return application_locale_;
+  }
   void set_application_locale(const std::string& locale) {
+    DCHECK(sequence_checker_.CalledOnValidSequence());
     application_locale_ = locale;
   }
 
   // The language list.
-  TranslateLanguageList* language_list() { return language_list_.get(); }
+  TranslateLanguageList* language_list() {
+    DCHECK(sequence_checker_.CalledOnValidSequence());
+    return language_list_.get();
+  }
 
   // The translate script.
-  TranslateScript* script() { return script_.get(); }
+  TranslateScript* script() {
+    DCHECK(sequence_checker_.CalledOnValidSequence());
+    return script_.get();
+  }
 
   // Let the caller decide if and when we should fetch the language list from
   // the translate server. This is a NOOP if prefs::kEnableTranslate is set to
   // false.
   static void RequestLanguageList(PrefService* prefs);
 
   // Fills |languages| with the list of languages that the translate server can
   // translate to and from.
   static void GetSupportedLanguages(std::vector<std::string>* languages);
 
@@ skipping 21 matching lines @@
   // Used by unit-tests to override some defaults:
   // Delay after which the translate script is fetched again from the
   // translation server.
   void SetTranslateScriptExpirationDelay(int delay_ms);
 
  private:
   friend struct base::DefaultSingletonTraits<TranslateDownloadManager>;
   TranslateDownloadManager();
   virtual ~TranslateDownloadManager();
 
+  // Validates that accesses to the download manager are performed on the same
+  // sequence.
+  base::SequenceChecker sequence_checker_;
+
   std::unique_ptr<TranslateLanguageList> language_list_;
 
   // An instance of TranslateScript which manages JavaScript source for
   // Translate.
   std::unique_ptr<TranslateScript> script_;
 
   std::string application_locale_;
   scoped_refptr<net::URLRequestContextGetter> request_context_;
 };
 
 }  // namespace translate
 
 #endif  // COMPONENTS_TRANSLATE_CORE_BROWSER_TRANSLATE_DOWNLOAD_MANAGER_H_