clang/win: Fix -Wextra warnings in webrtc.

webrtc/base/systeminfo.cc

 /*
  *  Copyright 2008 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 92 matching lines @@
 
 // Return the number of cpus available to the process.  Since affinity can be
 // changed on the fly, do not cache this value.
 // Can be affected by heat.
 int SystemInfo::GetCurCpus() {
   int cur_cpus = 0;
 #if defined(WEBRTC_WIN)
   DWORD_PTR process_mask = 0;
   DWORD_PTR system_mask = 0;
   ::GetProcessAffinityMask(::GetCurrentProcess(), &process_mask, &system_mask);
-  for (int i = 0; i < sizeof(DWORD_PTR) * 8; ++i) {
+  for (size_t i = 0; i < sizeof(DWORD_PTR) * 8; ++i) {
     if (process_mask & 1)
       ++cur_cpus;
     process_mask >>= 1;
   }
 #elif defined(WEBRTC_MAC)
   uint32_t sysctl_value;
   size_t length = sizeof(sysctl_value);
   int error = sysctlbyname("hw.ncpu", &sysctl_value, &length, NULL, 0);
   cur_cpus = !error ? static_cast<int>(sysctl_value) : 1;
 #else
@@ skipping 80 matching lines @@
   int error = sysctlbyname("hw.model", buffer, &length, NULL, 0);
   if (!error)
     return std::string(buffer, length - 1);
   return std::string();
 #else
   return "Not available";
 #endif
 }
 
 }  // namespace rtc