Add assertion to check that CPU profiling actually works.

src/platform-linux.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1190 matching lines @@
     SignalSender* sender = reinterpret_cast<SignalSender*>(raw_sender);
     sender->SendProfilingSignal(sampler->platform_data()->vm_tid());
   }
 
   void SendProfilingSignal(int tid) {
     if (!signal_handler_installed_) return;
     // Glibc doesn't provide a wrapper for tgkill(2).
 #if defined(ANDROID)
     syscall(__NR_tgkill, vm_tgid_, tid, SIGPROF);
 #else
-    syscall(SYS_tgkill, vm_tgid_, tid, SIGPROF);
+    int result = syscall(SYS_tgkill, vm_tgid_, tid, SIGPROF);
+    USE(result);
+    ASSERT(result == 0);
 #endif
   }
 
   void Sleep() {
     // Convert ms to us and subtract 100 us to compensate delays
     // occuring during signal delivery.
     useconds_t interval = interval_ * 1000 - 100;
 #if defined(ANDROID)
     usleep(interval);
 #else
@@ skipping 89 matching lines @@
 
 
 void Sampler::Stop() {
   ASSERT(IsActive());
   SignalSender::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 
 } }  // namespace v8::internal