Reland of write scopes of non-simple default arguments

src/parsing/parameter-initializer-rewriter.cc

Index: src/parsing/parameter-initializer-rewriter.cc
diff --git a/src/parsing/parameter-initializer-rewriter.cc b/src/parsing/parameter-initializer-rewriter.cc
index cbbf8deec7997c0f1bc5665c394c848ac3676baa..6362c63f8ec65863e97ffac96f362a1e6ced4c9d 100644
--- a/src/parsing/parameter-initializer-rewriter.cc
+++ b/src/parsing/parameter-initializer-rewriter.cc
@@ -90,6 +90,10 @@
   if (proxy->is_resolved()) {
     Variable* var = proxy->var();
     if (var->mode() != TEMPORARY) return;
+    // For rewriting inside the same ClosureScope (e.g., putting default
+    // parameter values in their own inner scope in certain cases), refrain
+    // from invalidly moving temporaries to a block scope.
+    if (var->scope()->ClosureScope() == new_scope_->ClosureScope()) return;
     int index = old_scope_->RemoveTemporary(var);
     if (index >= 0) {
       temps_.push_back(std::make_pair(var, index));