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

google_apis/drive/time_util.cc

 // Copyright (c) 2012 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 "google_apis/drive/time_util.h"
 
 #include <string>
 #include <vector>
 
 #include "base/strings/string_number_conversions.h"
@@ skipping 46 matching lines @@
         raw_value, "T", base::KEEP_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
     if (parts.size() != 2)
       return false;
     date = parts[0];
     time_and_tz = parts[1];
   }
 
   // Parses timezone suffix on the time part if available.
   {
     std::vector<base::StringPiece> parts;
-    if (time_and_tz[time_and_tz.size() - 1] == 'Z') {
+    if (time_and_tz.back() == 'Z') {
       // Timezone is 'Z' (UTC)
       has_timezone = true;
       offset_to_utc_in_minutes = 0;
       time = time_and_tz;
       time.remove_suffix(1);
     } else {
       parts = base::SplitStringPiece(
           time_and_tz, "+", base::KEEP_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
       if (parts.size() == 2) {
         // Timezone is "+hh:mm" format
@@ skipping 94 matching lines @@
   base::Time::Exploded exploded;
   time.LocalExplode(&exploded);
   return base::StringPrintf(
       "%04d-%02d-%02dT%02d:%02d:%02d.%03d",
       exploded.year, exploded.month, exploded.day_of_month,
       exploded.hour, exploded.minute, exploded.second, exploded.millisecond);
 }
 
 }  // namespace util
 }  // namespace google_apis