Fix VM profiler for simulator builds.

runtime/vm/profiler.cc

Index: runtime/vm/profiler.cc
diff --git a/runtime/vm/profiler.cc b/runtime/vm/profiler.cc
index dc1dc344e618090216ec61a3b5aaa62557622237..e9ad1ccfa0de04fc67062c904699b5e00d6f3dba 100644
--- a/runtime/vm/profiler.cc
+++ b/runtime/vm/profiler.cc
@@ -841,12 +841,9 @@ static bool GetAndValidateIsolateStackBounds(Isolate* isolate,
   ASSERT(stack_lower != NULL);
   ASSERT(stack_upper != NULL);
 #if defined(USING_SIMULATOR)
-  Simulator* simulator = NULL;
-#endif
-
-#if defined(USING_SIMULATOR)
   const bool in_dart_code = ExecutingDart(isolate);
   if (in_dart_code) {
+    Simulator* simulator = isolate->simulator();
     *stack_lower = simulator->StackBase();
     *stack_upper = simulator->StackTop();
   } else if (!isolate->GetProfilerStackBounds(stack_lower, stack_upper)) {