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

google_apis/drive/drive_api_requests.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/drive_api_requests.h"
 
 #include <stddef.h>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 201 matching lines @@
   base::StringPiece content_type_piece(content_type);
   if (!content_type_piece.starts_with(kMultipartMixedMimeTypePrefix)) {
     return false;
   }
   content_type_piece.remove_prefix(
       base::StringPiece(kMultipartMixedMimeTypePrefix).size());
 
   if (content_type_piece.empty())
     return false;
   if (content_type_piece[0] == '"') {
-    if (content_type_piece.size() <= 2 ||
-        content_type_piece[content_type_piece.size() - 1] != '"') {
+    if (content_type_piece.size() <= 2 || content_type_piece.back() != '"')
       return false;
-    }
+
     content_type_piece =
         content_type_piece.substr(1, content_type_piece.size() - 2);
   }
 
   std::string boundary;
   content_type_piece.CopyToString(&boundary);
   const std::string header = "--" + boundary;
   const std::string terminator = "--" + boundary + "--";
 
   std::vector<base::StringPiece> lines;
@@ skipping 1215 matching lines @@
     } else if (last_progress_value_ < child->data_offset + child->data_size &&
                child->data_offset + child->data_size < current) {
       child->request->NotifyUploadProgress(source, child->data_size,
                                            child->data_size);
     }
   }
   last_progress_value_ = current;
 }
 }  // namespace drive
 }  // namespace google_apis