FetchMore functionality backend

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 298 matching lines @@
         << "Unknown value for " << kPersonalizationName << ": "
         << personalization;
   }
 }
 
 NTPSnippetsFetcher::~NTPSnippetsFetcher() {
   if (waiting_for_refresh_token_)
     token_service_->RemoveObserver(this);
 }
 
-void NTPSnippetsFetcher::SetCallback(
-    const SnippetsAvailableCallback& callback) {
-  snippets_available_callback_ = callback;
+void NTPSnippetsFetcher::SetCallback(SnippetsAvailableCallback callback) {
+  snippets_available_callback_ = std::move(callback);
 }
 
 void NTPSnippetsFetcher::FetchSnippetsFromHosts(
     const std::set<std::string>& hosts,
     const std::string& language_code,
     const std::set<std::string>& excluded_ids,
     int count,
     bool interactive_request) {
   if (!DemandQuotaForRequest(interactive_request)) {
     FetchFinished(OptionalFetchedCategories(),
@@ skipping 431 matching lines @@
   if (!IsFetchPreconditionFailed(result)) {
     UMA_HISTOGRAM_TIMES("NewTabPage.Snippets.FetchTime",
                         tick_clock_->NowTicks() - fetch_start_time_);
   }
   UMA_HISTOGRAM_ENUMERATION("NewTabPage.Snippets.FetchResult",
                             static_cast<int>(result),
                             static_cast<int>(FetchResult::RESULT_MAX));
 
   DVLOG(1) << "Fetch finished: " << last_status_;
   if (!snippets_available_callback_.is_null())
-    snippets_available_callback_.Run(std::move(fetched_categories));
+    std::move(snippets_available_callback_).Run(std::move(fetched_categories));
 }
 
 bool NTPSnippetsFetcher::DemandQuotaForRequest(bool interactive_request) {
   switch (user_classifier_->GetUserClass()) {
     case UserClassifier::UserClass::RARE_NTP_USER:
       return request_throttler_rare_ntp_user_.DemandQuotaForRequest(
           interactive_request);
     case UserClassifier::UserClass::ACTIVE_NTP_USER:
       return request_throttler_active_ntp_user_.DemandQuotaForRequest(
           interactive_request);
     case UserClassifier::UserClass::ACTIVE_SUGGESTIONS_CONSUMER:
       return request_throttler_active_suggestions_consumer_
           .DemandQuotaForRequest(interactive_request);
   }
   NOTREACHED();
   return false;
 }
 
 }  // namespace ntp_snippets