Fixed all unused-variable Clang warnings on Windows.

cloud_print/virtual_driver/win/virtual_driver_helpers.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 "cloud_print/virtual_driver/win/virtual_driver_helpers.h"
 
 #include <windows.h>
 #include <winspool.h>
 
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/strings/string16.h"
 #include "base/win/windows_version.h"
 #include "cloud_print/common/win/cloud_print_utils.h"
 
 namespace cloud_print {
 
-const size_t kMaxMessageLen = 100;
-
 void DisplayWindowsMessage(HWND hwnd, HRESULT hr,
                            const base::string16 &caption) {
   ::MessageBox(hwnd, GetErrorMessage(hr).c_str(), caption.c_str(), MB_OK);
 }
 
 base::string16 GetPortMonitorDllName() {
   if (IsSystem64Bit()) {
     return base::string16(L"gcp_portmon64.dll");
   } else {
     return base::string16(L"gcp_portmon.dll");
@@ skipping 22 matching lines @@
 
 bool IsSystem64Bit() {
   base::win::OSInfo::WindowsArchitecture arch =
       base::win::OSInfo::GetInstance()->architecture();
   return (arch == base::win::OSInfo::X64_ARCHITECTURE) ||
          (arch == base::win::OSInfo::IA64_ARCHITECTURE);
 }
 
 }