Fix warning so Android ipc_tests builds again. (-Werror turned on in http://codereview.chromium.org…

ipc/ipc_channel_posix.cc

 // Copyright (c) 2011 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 "ipc/ipc_channel_posix.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <stddef.h>
 #include <sys/types.h>
@@ skipping 950 matching lines @@
   return true;
 #elif defined(OS_SOLARIS)
   return false;
 #else
   struct ucred cred;
   socklen_t cred_len = sizeof(cred);
   if (getsockopt(pipe_, SOL_SOCKET, SO_PEERCRED, &cred, &cred_len) != 0) {
     PLOG(ERROR) << "getsockopt " << pipe_;
     return false;
   }
-  if (cred_len < sizeof(cred)) {
+  if (static_cast<unsigned>(cred_len) < sizeof(cred)) {
     NOTREACHED() << "Truncated ucred from SO_PEERCRED?";
     return false;
   }
   *client_euid = cred.uid;
   return true;
 #endif
 }
 
 void Channel::ChannelImpl::ResetToAcceptingConnectionState() {
   // Unregister libevent for the unix domain socket and close it.
@@ skipping 271 matching lines @@
 }
 
 #if defined(OS_LINUX)
 // static
 void Channel::SetGlobalPid(int pid) {
   ChannelImpl::SetGlobalPid(pid);
 }
 #endif  // OS_LINUX
 
 }  // namespace IPC