Remove some PlatformFile instances from ChromeOS Drive.

chrome/browser/chromeos/drive/drive_file_stream_reader.cc

 // Copyright 2013 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_file_stream_reader.h"
 
 #include <algorithm>
 #include <cstring>
 
 #include "base/callback_helpers.h"
@@ skipping 101 matching lines @@
 int LocalReaderProxy::Read(net::IOBuffer* buffer, int buffer_length,
                            const net::CompletionCallback& callback) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   DCHECK(file_reader_);
 
   if (buffer_length > remaining_length_) {
     // Here, narrowing is safe.
     buffer_length = static_cast<int>(remaining_length_);
   }
 
+  if (!buffer_length)
+    return 0;
+
   file_reader_->Read(buffer, buffer_length,
                      base::Bind(&LocalReaderProxy::OnReadCompleted,
                                 weak_ptr_factory_.GetWeakPtr(), callback));
   return net::ERR_IO_PENDING;
 }
 
 void LocalReaderProxy::OnGetContent(scoped_ptr<std::string> data) {
   // This method should never be called, because no data should be received
   // from the network during the reading of local-cache file.
   NOTREACHED();
@@ skipping 331 matching lines @@
     // Note: due to the same reason, LocalReaderProxy::OnCompleted may
     // or may not be called. This is timing issue, and it is difficult to avoid
     // unfortunately.
     if (error != FILE_ERROR_OK) {
       callback.Run(FileErrorToNetError(error), scoped_ptr<ResourceEntry>());
     }
   }
 }
 
 }  // namespace drive