Introduce --zap-cpp-pointers (off by default)

src/execution.cc

Index: src/execution.cc
diff --git a/src/execution.cc b/src/execution.cc
index 05a69acfdedcc2099500060d84f2f7ad41b7098b..922211a3161dccefd6c9f335e921c4eed3f5dd25 100644
--- a/src/execution.cc
+++ b/src/execution.cc
@@ -60,6 +60,10 @@ MUST_USE_RESULT MaybeHandle<Object> Invoke(
     Handle<Object> receiver, int argc, Handle<Object> args[],
     Handle<Object> new_target, Execution::MessageHandling message_handling) {
   DCHECK(!receiver->IsJSGlobalObject());
+#if DEBUG
+  // Assume that any JS call can allocate.
+  if (FLAG_zap_cpp_pointers) ZapHeapPointersInCppFrames(isolate);
+#endif
 
 #ifdef USE_SIMULATOR
   // Simulators use separate stacks for C++ and JS. JS stack overflow checks
@@ -418,8 +422,12 @@ bool StackGuard::ThreadLocal::Initialize(Isolate* isolate) {
   bool should_set_stack_limits = false;
   if (real_climit_ == kIllegalLimit) {
     const uintptr_t kLimitSize = FLAG_stack_size * KB;
-    DCHECK(GetCurrentStackPosition() > kLimitSize);
-    uintptr_t limit = GetCurrentStackPosition() - kLimitSize;
+    uintptr_t current_stack_position = GetCurrentStackPosition();
+#if DEBUG
+    DCHECK(current_stack_position > kLimitSize);
+    stack_base_position_ = current_stack_position;
+#endif
+    uintptr_t limit = current_stack_position - kLimitSize;
     real_jslimit_ = SimulatorStack::JsLimitFromCLimit(isolate, limit);
     set_jslimit(SimulatorStack::JsLimitFromCLimit(isolate, limit));
     real_climit_ = limit;