Fix prctl ERROR messages on Linux debug builds.

base/threading/platform_thread_posix.cc

Index: base/threading/platform_thread_posix.cc
diff --git a/base/threading/platform_thread_posix.cc b/base/threading/platform_thread_posix.cc
index 1d72f07fc645b3b7e087c751b148f2a3833ea0d0..b6cb7a51f38cf0f383aa5b14543e971574e705ed 100644
--- a/base/threading/platform_thread_posix.cc
+++ b/base/threading/platform_thread_posix.cc
@@ -190,10 +190,11 @@ void PlatformThread::SetName(const char* name) {
   // http://0pointer.de/blog/projects/name-your-threads.html
   // Set the name for the LWP (which gets truncated to 15 characters).
   // Note that glibc also has a 'pthread_setname_np' api, but it may not be
-  // available everywhere and doesn't seem to have any advantage over using
-  // prctl.
+  // available everywhere and it's only benefit over using prctl directly is
+  // that it can set the name of threads other than the current thread.
   int err = prctl(PR_SET_NAME, name);
-  if (err < 0)
+  // We expect EPERM failures in sandboxed processes, just ignore those.
+  if (err < 0 && errno != EPERM)
     DPLOG(ERROR) << "prctl(PR_SET_NAME)";
 }
 #elif defined(OS_MACOSX)