Reland^3 r22105 "Remove static initializer from isolate"

src/sampler.cc

Index: src/sampler.cc
diff --git a/src/sampler.cc b/src/sampler.cc
index 7ee7216c2fdbfe83f8cae8bba71763cf11381b5d..f89978f1be6ff5f3d6e29e0f57b2a55dc3b72620 100644
--- a/src/sampler.cc
+++ b/src/sampler.cc
@@ -331,7 +331,7 @@ void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
 #else
   USE(info);
   if (signal != SIGPROF) return;
-  Isolate* isolate = Isolate::UncheckedCurrent();
+  Isolate* isolate = Isolate::UnsafeCurrent();
   if (isolate == NULL || !isolate->IsInitialized() || !isolate->IsInUse()) {
     // We require a fully initialized and entered isolate.
     return;