[Isolates] linux: fix sampling profiler.

src/platform-linux.cc

Index: src/platform-linux.cc
diff --git a/src/platform-linux.cc b/src/platform-linux.cc
index 1de74164479f4a20230a52194b0f9f65cf5fe41a..d830cb034e8b726ed517c530677a10265f911c35 100644
--- a/src/platform-linux.cc
+++ b/src/platform-linux.cc
@@ -810,7 +810,10 @@ static void ProfilerSignalHandler(int signal, siginfo_t* info, void* context) {
   USE(info);
   if (signal != SIGPROF) return;
   Isolate* isolate = Isolate::UncheckedCurrent();
-  if (isolate == NULL || !isolate->IsInUse()) return;
+  if (isolate == NULL || !isolate->IsInitialized() || !isolate->IsInUse()) {
+    // We require a fully initialized and entered isolate.
+    return;
+  }
   Sampler* sampler = isolate->logger()->sampler();
   if (sampler == NULL || !sampler->IsActive()) return;
 
@@ -882,7 +885,7 @@ class SignalSender : public Thread {
       sigemptyset(&sa.sa_mask);
       sa.sa_flags = SA_RESTART | SA_SIGINFO;
       signal_handler_installed_ =
-          (sigaction(SIGPROF, &sa, &old_signal_handler_) != 0);
+          (sigaction(SIGPROF, &sa, &old_signal_handler_) == 0);
 
       // Start a thread that sends SIGPROF signal to VM threads.
       instance_ = new SignalSender(sampler->interval());