Use container::back() and container::pop_back().

headless/public/util/error_reporter.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 "headless/public/util/error_reporter.h"
 
 #include <sstream>
 
 #include "base/logging.h"
 
 namespace headless {
 
 ErrorReporter::ErrorReporter() {}
 
 ErrorReporter::~ErrorReporter() {}
 
 void ErrorReporter::Push() {
   path_.push_back(nullptr);
 }
 
 void ErrorReporter::Pop() {
   path_.pop_back();
 }
 
 void ErrorReporter::SetName(const char* name) {
   DCHECK(!path_.empty());
-  path_[path_.size() - 1] = name;
+  path_.back() = name;
 }
 
 void ErrorReporter::AddError(base::StringPiece description) {
   std::stringstream error;
   for (size_t i = 0; i < path_.size(); i++) {
     if (!path_[i]) {
       DCHECK_EQ(i + 1, path_.size());
       break;
     }
     if (i)
       error << '.';
     error << path_[i];
   }
   if (error.tellp())
     error << ": ";
   error << description;
   errors_.push_back(error.str());
 }
 
 bool ErrorReporter::HasErrors() const {
   return !errors_.empty();
 }
 
 }  // namespace headless