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

net/tools/flip_server/balsa_headers.h

 // Copyright (c) 2009 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.
 
 #ifndef NET_TOOLS_FLIP_SERVER_BALSA_HEADERS_H_
 #define NET_TOOLS_FLIP_SERVER_BALSA_HEADERS_H_
 #pragma once
 
 #include <algorithm>
 #include <iosfwd>
@@ skipping 798 matching lines @@
   // append additional header lines to the header without copying the header.
   // When the user is done with appending to the buffer,
   // WriteHeaderEndingToBuffer must be used to terminate the HTTP
   // header in the buffer. This method is a no-op if key is empty.
   template <typename Buffer>
   static void WriteHeaderLineToBuffer(Buffer* buffer,
                                       const base::StringPiece& key,
                                       const base::StringPiece& value) {
     // if the key is empty, we don't want to write the rest because it
     // will not be a well-formed header line.
-    if (key.size() > 0) {
+    if (!key.empty()) {
       buffer->Write(key.data(), key.size());
       buffer->Write(": ", 2);
       buffer->Write(value.data(), value.size());
       buffer->Write("\r\n", 2);
     }
   }
 
   // Dump the textural representation of the header object to a string, which
   // is suitable for writing out to logs. All CRLF will be printed out as \n.
   // This function can be called on a header object in any state. Raw header
@@ skipping 307 matching lines @@
   size_t end_of_firstline_idx_;
 
   bool transfer_encoding_is_chunked_;
 
   HeaderLines header_lines_;
 };
 
 }  // namespace net
 
 #endif  // NET_TOOLS_FLIP_SERVER_BALSA_HEADERS_H_