Fixes an invalidated pointer access in NTPSnipppetsFetcher.

components/ntp_snippets/content_suggestions_service_unittest.cc

 // Copyright 2016 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 "components/ntp_snippets/content_suggestions_service.h"
 
 #include <memory>
 #include <utility>
 #include <vector>
 
@@ skipping 74 matching lines @@
     observer()->OnSuggestionInvalidated(this, suggestion_id);
   }
 
   MOCK_METHOD3(ClearHistory,
                void(base::Time begin,
                     base::Time end,
                     const base::Callback<bool(const GURL& url)>& filter));
   MOCK_METHOD3(Fetch,
                void(const Category&,
                     const std::set<std::string>&,
-                    FetchingCallback));
+                    const FetchingCallback&));
   MOCK_METHOD1(ClearCachedSuggestions, void(Category category));
   MOCK_METHOD2(GetDismissedSuggestionsForDebugging,
                void(Category category,
                     const DismissedSuggestionsCallback& callback));
   MOCK_METHOD1(ClearDismissedSuggestionsForDebugging, void(Category category));
   MOCK_METHOD1(DismissSuggestion,
                void(const ContentSuggestion::ID& suggestion_id));
   MOCK_METHOD2(FetchSuggestionImage,
                void(const ContentSuggestion::ID& suggestion_id,
                     const ImageFetchedCallback& callback));
@@ skipping 594 matching lines @@
   provider = RegisterProvider(category);
   provider->FireCategoryStatusChangedWithCurrentStatus(category);
   EXPECT_TRUE(service()->IsCategoryDismissed(category));
 
   service()->RestoreDismissedCategories();
   EXPECT_FALSE(service()->IsCategoryDismissed(category));
   EXPECT_THAT(providers().find(category)->second, Eq(provider));
 }
 
 }  // namespace ntp_snippets