Use a custom Struct for stack trace storage

src/execution.cc

Index: src/execution.cc
diff --git a/src/execution.cc b/src/execution.cc
index 709c13df7340c21d74ef78cf11fafa34d92d775c..56c08b5b53679d44e4adaa9652f460b5c5492817 100644
--- a/src/execution.cc
+++ b/src/execution.cc
@@ -434,31 +434,6 @@ void StackGuard::InitThread(const ExecutionAccess& lock) {
 // --- C a l l s   t o   n a t i v e s ---
 
 
-Handle<String> Execution::GetStackTraceLine(Handle<Object> recv,
-                                            Handle<JSFunction> fun,
-                                            Handle<Object> pos,
-                                            Handle<Object> is_global) {
-  Isolate* isolate = fun->GetIsolate();
-  Handle<Object> strict_mode = isolate->factory()->ToBoolean(false);
-
-  MaybeHandle<Object> maybe_callsite =
-      CallSiteUtils::Construct(isolate, recv, fun, pos, strict_mode);
-  if (maybe_callsite.is_null()) {
-    isolate->clear_pending_exception();
-    return isolate->factory()->empty_string();
-  }
-
-  MaybeHandle<String> maybe_to_string =
-      CallSiteUtils::ToString(isolate, maybe_callsite.ToHandleChecked());
-  if (maybe_to_string.is_null()) {
-    isolate->clear_pending_exception();
-    return isolate->factory()->empty_string();
-  }
-
-  return maybe_to_string.ToHandleChecked();
-}
-
-
 void StackGuard::HandleGCInterrupt() {
   if (CheckAndClearInterrupt(GC_REQUEST)) {
     isolate_->heap()->HandleGCRequest();