Style fixes in //ios

ios/web/public/user_agent.mm

 // Copyright 2014 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 "ios/web/public/user_agent.h"
 
 #import <UIKit/UIKit.h>
 
 #include <sys/sysctl.h>
 #include <string>
@@ skipping 90 matching lines @@
 
 }  // namespace
 
 namespace web {
 
 std::string BuildUserAgentFromProduct(const std::string& product) {
   // Retrieve the kernel build number.
   int mib[2] = {CTL_KERN, KERN_OSVERSION};
   unsigned int namelen = sizeof(mib) / sizeof(mib[0]);
   size_t bufferSize = 0;
-  sysctl(mib, namelen, NULL, &bufferSize, NULL, 0);
+  sysctl(mib, namelen, nullptr, &bufferSize, nullptr, 0);
   char kernel_version[bufferSize];
-  int result = sysctl(mib, namelen, kernel_version, &bufferSize, NULL, 0);
+  int result = sysctl(mib, namelen, kernel_version, &bufferSize, nullptr, 0);
   DCHECK(result == 0);
 
   UAVersions ua_versions = GetUAVersionsForCurrentOS();
 
   std::string user_agent;
   base::StringAppendF(&user_agent,
                       "Mozilla/5.0 (%s) AppleWebKit/%s"
                       " (KHTML, like Gecko) %s Mobile/%s Safari/%s",
                       BuildOSCpuInfo().c_str(),
                       ua_versions.webkit_version_string,
                       product.c_str(),
                       kernel_version,
                       ua_versions.safari_version_string);
 
   return user_agent;
 }
 
 }  // namespace web