Fixes an invalidated pointer access in NTPSnipppetsFetcher.

components/ntp_snippets/remote/ntp_snippets_fetcher.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/remote/ntp_snippets_fetcher.h"
 
 #include <cstdlib>
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
@@ skipping 756 matching lines @@
   Category exclusive = params_.exclusive_category.value();
   auto category_it =
       std::find_if(categories->begin(), categories->end(),
                    [&exclusive](const FetchedCategory& c) -> bool {
                      return c.category == exclusive;
                    });
   if (category_it == categories->end()) {
     categories->clear();
     return;
   }
-  categories->erase(categories->begin(), category_it);
-  categories->erase(category_it + 1, categories->end());
+  FetchedCategory category = std::move(*category_it);
+  categories->clear();
+  categories->emplace_back(std::move(category));
 }
 
 void NTPSnippetsFetcher::FetchFinished(
     OptionalFetchedCategories fetched_categories,
     FetchResult result,
     const std::string& extra_message) {
   DCHECK(result == FetchResult::SUCCESS || !fetched_categories);
   last_status_ = FetchResultToString(result) + extra_message;
 
-  // TODO(fhorschig): Filter (un)wanted categories by modifying fetch request.
-  // As soon as backends support the parameter, there is no reason to overfetch
-  // and filter here.
+  // Filter out unwanted categories if necessary.
+  // TODO(fhorschig): As soon as the server supports filtering by
+  // that instead of over-fetching and filtering here.
   if (fetched_categories.has_value())
     FilterCategories(&fetched_categories.value());
 
   // Don't record FetchTimes if the result indicates that a precondition
   // failed and we never actually sent a network request
   if (!IsFetchPreconditionFailed(result)) {
     UMA_HISTOGRAM_TIMES("NewTabPage.Snippets.FetchTime",
                         tick_clock_->NowTicks() - fetch_start_time_);
   }
   UMA_HISTOGRAM_ENUMERATION("NewTabPage.Snippets.FetchResult",
@@ skipping 15 matching lines @@
           interactive_request);
     case UserClassifier::UserClass::ACTIVE_SUGGESTIONS_CONSUMER:
       return request_throttler_active_suggestions_consumer_
           .DemandQuotaForRequest(interactive_request);
   }
   NOTREACHED();
   return false;
 }
 
 }  // namespace ntp_snippets