Inject JSON parsing in WebResource as a callback rather than inheritance

components/web_resource/web_resource_service.h

 // Copyright 2012 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_WEB_RESOURCE_WEB_RESOURCE_SERVICE_H_
 #define COMPONENTS_WEB_RESOURCE_WEB_RESOURCE_SERVICE_H_
 
 #include <string>
 
+#include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "components/web_resource/resource_request_allowed_notifier.h"
 #include "net/url_request/url_fetcher_delegate.h"
 #include "url/gurl.h"
 
 class PrefService;
 
 namespace base {
 class DictionaryValue;
 class Value;
 }
 
 namespace net {
 class URLFetcher;
 class URLRequestContextGetter;
 }
 
 namespace web_resource {
 
 // A WebResourceService fetches JSON data from a web server and periodically
 // refreshes it.
 class WebResourceService
     : public net::URLFetcherDelegate,
       public ResourceRequestAllowedNotifier::Observer {
  public:
+  // Callbacks for JSON parsing.
+  using SuccessCallback = base::Callback<void(scoped_ptr<base::Value>)>;
+  using ErrorCallback = base::Callback<void(const std::string&)>;
+  using ParseJSONCallback = base::Callback<
+      void(const std::string&, const SuccessCallback&, const ErrorCallback&)>;
+
   // Creates a new WebResourceService.
   // If |application_locale| is not empty, it will be appended as a locale
   // parameter to the resource URL.
   WebResourceService(PrefService* prefs,
                      const GURL& web_resource_server,
                      const std::string& application_locale,  // May be empty
                      const char* last_update_time_pref_name,
                      int start_fetch_delay_ms,
                      int cache_update_delay_ms,
                      net::URLRequestContextGetter* request_context,
-                     const char* disable_network_switch);
+                     const char* disable_network_switch,
+                     const ParseJSONCallback& parse_json_callback);
 
   ~WebResourceService() override;
 
   // Sleep until cache needs to be updated, but always for at least
   // |start_fetch_delay_ms| so we don't interfere with startup.
   // Then begin updating resources.
   void StartAfterDelay();
 
  protected:
-  // Callbacks for JSON parsing.
-  using SuccessCallback = base::Callback<void(scoped_ptr<base::Value>)>;
-  using ErrorCallback = base::Callback<void(const std::string&)>;
-
   PrefService* prefs_;
 
  private:
   // For the subclasses to process the result of a fetch.
   virtual void Unpack(const base::DictionaryValue& parsed_json) = 0;
 
-  // Parses a JSON string |data| and invokes |success_callback| or
-  // |error_callback|.
-  virtual void ParseJSON(const std::string& data,
-                         const SuccessCallback& success_callback,
-                         const ErrorCallback& error_callback) = 0;
-
   // net::URLFetcherDelegate implementation:
   void OnURLFetchComplete(const net::URLFetcher* source) override;
 
   // Schedules a fetch after |delay_ms| milliseconds.
   void ScheduleFetch(int64 delay_ms);
 
   // Starts fetching data from the server.
   void StartFetch();
 
   // Set |in_fetch_| to false, clean up temp directories (in the future).
@@ skipping 30 matching lines @@
   // Delay on first fetch so we don't interfere with startup.
   int start_fetch_delay_ms_;
 
   // Delay between calls to update the web resource cache. This delay may be
   // different for different builds of Chrome.
   int cache_update_delay_ms_;
 
   // The request context for the resource fetch.
   scoped_refptr<net::URLRequestContextGetter> request_context_;
 
+  // Callback used to parse JSON.
+  ParseJSONCallback parse_json_callback_;
+
   // So that we can delay our start so as not to affect start-up time; also,
   // so that we can schedule future cache updates.
   base::WeakPtrFactory<WebResourceService> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WebResourceService);
 };
 
 }  // namespace web_resource
 
 #endif  // COMPONENTS_WEB_RESOURCE_WEB_RESOURCE_SERVICE_H_