drive: Change EventLogger to take printf format

chrome/browser/chromeos/drive/drive_prefetcher.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/drive_prefetcher.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/stringprintf.h"
 #include "chrome/browser/chromeos/drive/drive_file_system_interface.h"
@@ skipping 86 matching lines @@
   // Scans the filesystem. When it is finished, DoPrefetch() will be called.
   VisitDirectory(util::GetDriveMyDriveRootPath());
 }
 
 void DrivePrefetcher::DoPrefetch() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   for (LatestFileSet::reverse_iterator it = latest_files_.rbegin();
       it != latest_files_.rend(); ++it) {
     const std::string& resource_id = it->resource_id();
-    event_logger_->Log("Prefetcher: Enqueue prefetching " + resource_id);
+    event_logger_->Log("Prefetcher: Enqueue prefetching %s",
+                       resource_id.c_str());
     file_system_->GetFileByResourceId(
         resource_id,
         DriveClientContext(PREFETCH),
         base::Bind(&DrivePrefetcher::OnPrefetchFinished,
                    weak_ptr_factory_.GetWeakPtr(),
                    resource_id),
         google_apis::GetContentCallback());
   }
 }
 
 void DrivePrefetcher::OnPrefetchFinished(const std::string& resource_id,
                                          DriveFileError error,
                                          const base::FilePath& file_path,
                                          const std::string& mime_type,
                                          DriveFileType file_type) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   if (error != DRIVE_FILE_OK)
     LOG(WARNING) << "Prefetch failed: " << DriveFileErrorToString(error);
-  event_logger_->Log(base::StringPrintf("Prefetcher: Finish fetching (%s) %s",
-                                        DriveFileErrorToString(error).c_str(),
-                                        resource_id.c_str()));
+  event_logger_->Log("Prefetcher: Finish fetching (%s) %s",
+                     DriveFileErrorToString(error).c_str(),
+                     resource_id.c_str());
 }
 
 void DrivePrefetcher::VisitFile(const DriveEntryProto& entry) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   // Excessively large files will not be fetched.
   if (entry.file_info().size() > prefetch_file_size_limit_)
     return;
 
   // Remember the file in the set ordered by the |last_accessed| field.
@@ skipping 47 matching lines @@
 
 void DrivePrefetcher::OnReadDirectoryFinished() {
   DCHECK(number_of_inflight_traversals_ > 0);
 
   --number_of_inflight_traversals_;
   if (number_of_inflight_traversals_ == 0)
     DoPrefetch();  // Start prefetching.
 }
 
 }  // namespace drive