Change other usages of .size() to .empty() when applicable.

chrome/browser/autocomplete/history_contents_provider.cc

 // Copyright (c) 2010 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 "chrome/browser/autocomplete/history_contents_provider.h"
 
 #include "base/callback.h"
 #include "base/metrics/histogram.h"
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
@@ skipping 95 matching lines @@
     // get marked up for this new input.  In synchronous_only mode, cancel the
     // history query.
     if (input.synchronous_only()) {
       done_ = true;
       request_consumer_.CancelAllRequests();
     }
     ConvertResults();
     return;
   }
 
-  if (results_.size() != 0) {
+  if (!results_.empty()) {
     // Clear the results. We swap in an empty one as the easy way to clear it.
     history::QueryResults empty_results;
     results_.Swap(&empty_results);
   }
 
   // Querying bookmarks is synchronous, so we always do it.
   QueryBookmarks(input);
 
   // Convert the bookmark results.
   ConvertResults();
@@ skipping 145 matching lines @@
   UMA_HISTOGRAM_TIMES("Omnibox.QueryBookmarksTime",
                       TimeTicks::Now() - start_time);
 }
 
 void HistoryContentsProvider::AddBookmarkTitleMatchToResults(
     const bookmark_utils::TitleMatch& match) {
   history::URLResult url_result(match.node->GetURL(), match.match_positions);
   url_result.set_title(match.node->GetTitle());
   results_.AppendURLBySwapping(&url_result);
 }