drive: Change EventLogger to take printf format

chrome/browser/chromeos/drive/event_logger.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 "chrome/browser/chromeos/drive/event_logger.h"
 
+#include "base/stringprintf.h"
+
 namespace drive {
 
 EventLogger::Event::Event(int id, const std::string& what)
     : id(id),
       when(base::Time::Now()),
       what(what) {
 }
 
 EventLogger::EventLogger(size_t history_size)
     : history_size_(history_size),
       next_event_id_(0) {
 }
 
 EventLogger::~EventLogger() {
 }
 
-void EventLogger::Log(const std::string& what) {
+void EventLogger::Log(const char* format, ...) {
+  std::string what;
+
+  va_list args;
+  va_start(args, format);
+  base::StringAppendV(&what, format, args);
+  va_end(args);
+
   history_.push_back(Event(next_event_id_, what));
   ++next_event_id_;
   if (history_.size() > history_size_)
     history_.pop_front();
 }
 
 }  // namespace drive