Fix linux/gcc compiler warnings in tools/ipc_fuzzer.

tools/ipc_fuzzer/message_lib/message_file_writer.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 <limits.h>
 #include <set>
 
 #include "base/logging.h"
 #include "base/platform_file.h"
 #include "tools/ipc_fuzzer/message_lib/message_file.h"
@@ skipping 61 matching lines @@
     return false;
   }
   return true;
 }
 
 bool Writer::WriteBlob(const void *buffer, size_t size) {
   if (size > INT_MAX)
     return false;
   const char* char_buffer = static_cast<const char*>(buffer);
   int ret = base::WritePlatformFileAtCurrentPos(file_, char_buffer, size);
-  if (ret != size) {
+  if (ret != static_cast<int>(size)) {
     LOG(ERROR) << "Failed to write " << size << " bytes.";
     return false;
   }
   return true;
 }
 
 bool Writer::CollectMessageTypes() {
   for (size_t i = 0; i < messages_->size(); ++i) {
     uint32_t type = (*messages_)[i]->type();
     if (!MessageNames::GetInstance()->TypeExists(type)) {
@@ skipping 74 matching lines @@
 
 }  // namespace
 
 bool MessageFile::Write(const base::FilePath& path,
                         const MessageVector& messages) {
   Writer writer(path);
   return writer.Write(messages);
 }
 
 }  // namespace ipc_fuzzer