Add StringPrintV, fix libxml_utils.cc to use it

chrome/common/libxml_utils.cc

 // 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.
 
 #include "chrome/common/libxml_utils.h"
 
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/string_util.h"
 
@@ skipping 17 matching lines @@
   if (reader_)
     xmlFreeTextReader(reader_);
 }
 
 // static
 void XmlReader::GenericErrorCallback(void* context, const char* msg, ...) {
   va_list args;
   va_start(args, msg);
 
   XmlReader* reader = static_cast<XmlReader*>(context);
-  reader->errors_.append(StringPrintf(msg, args));
+  reader->errors_.append(StringPrintV(msg, args));
+  va_end(args);
 }
 
 bool XmlReader::Load(const std::string& input) {
   const int kParseOptions = XML_PARSE_RECOVER |  // recover on errors
                             XML_PARSE_NONET;     // forbid network access
   // TODO(evanm): Verify it's OK to pass NULL for the URL and encoding.
   // The libxml code allows for these, but it's unclear what effect is has.
   reader_ = xmlReaderForMemory(input.data(), static_cast<int>(input.size()),
                                NULL, NULL, kParseOptions);
   return reader_ != NULL;
@@ skipping 84 matching lines @@
   writer_ = xmlNewTextWriterMemory(buffer_, 0);
   xmlTextWriterSetIndent(writer_, 1);
   xmlTextWriterStartDocument(writer_, NULL, NULL, NULL);
 }
 
 void XmlWriter::StopWriting() {
   xmlTextWriterEndDocument(writer_);
   xmlFreeTextWriter(writer_);
   writer_ = NULL;
 }