[parser] Create arrow function scopes while parsing the head

This simplifies NextArrowFunctionInfo, allows us to Scope::Snapshot::Reparent
directly rather than moving it, and allows us to skip reparenting in the simple
parameter arrow function cases.

This is a reland of https://chromium-review.googlesource.com/c/v8/v8/+/1397664,
simply splitting out the arrow-function-name-inferring part.

Change-Id: I640d911a9607edc3bbb0e5ff3bf992094e4159e4
Reviewed-on: https://chromium-review.googlesource.com/c/1397701Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58570}

src/ast/scopes.cc

@@ -888,11 +888,15 @@ void Scope::Snapshot::Reparent(DeclarationScope* new_parent) {
   outer_closure->locals_.Rewind(top_local_);
 
   // Move eval calls since Snapshot's creation into new_parent.
-  if (outer_scope_and_calls_eval_.GetPayload()) {
+  if (outer_scope_and_calls_eval_->scope_calls_eval_) {
     new_parent->scope_calls_eval_ = true;
     new_parent->inner_scope_calls_eval_ = true;
   }
 
+  // We are in the arrow function case. The calls eval we may have recorded
+  // is intended for the inner scope and we should simply restore the
+  // original "calls eval" flag of the outer scope.
+  RestoreEvalFlag();
   Clear();
 }
 

src/ast/scopes.h

@@ -147,24 +147,6 @@ class V8_EXPORT_PRIVATE Scope : public NON_EXPORTED_BASE(ZoneObject) {
           outer_scope_and_calls_eval_.GetPayload();
     }
 
-    Snapshot& operator=(Snapshot&& source) V8_NOEXCEPT {
-      outer_scope_and_calls_eval_.SetPointer(
-          source.outer_scope_and_calls_eval_.GetPointer());
-      outer_scope_and_calls_eval_.SetPayload(
-          outer_scope_and_calls_eval_->scope_calls_eval_);
-      top_inner_scope_ = source.top_inner_scope_;
-      top_unresolved_ = source.top_unresolved_;
-      top_local_ = source.top_local_;
-
-      // We are in the arrow function case. The calls eval we may have recorded
-      // is intended for the inner scope and we should simply restore the
-      // original "calls eval" flag of the outer scope.
-      source.RestoreEvalFlag();
-      source.Clear();
-
-      return *this;
-    }
-
     void Reparent(DeclarationScope* new_parent);
     bool IsCleared() const {
       return outer_scope_and_calls_eval_.GetPointer() == nullptr;