[ast] Don't assume declaration scopes are never removed.

src/ast/scopes.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ast/scopes.h"
 
 #include <set>
 
 #include "src/accessors.h"
 #include "src/ast/ast.h"
@@ skipping 620 matching lines @@
     NonLocal(name, DYNAMIC);
   } else {
     variables_.Add(zone(), function_);
   }
   return function_;
 }
 
 bool Scope::HasBeenRemoved() const {
   // TODO(neis): Store this information somewhere instead of calculating it.
 
-  if (!is_block_scope() || is_declaration_scope()) return false;
+  if (!is_block_scope()) return false;  // Shortcut.
 
   Scope* parent = outer_scope();
   if (parent == nullptr) {
     DCHECK(is_script_scope());
     return false;
   }
 
   Scope* sibling = parent->inner_scope();
   for (; sibling != nullptr; sibling = sibling->sibling()) {
     if (sibling == this) return false;
@@ skipping 1378 matching lines @@
   Variable* function =
       is_function_scope() ? AsDeclarationScope()->function_var() : nullptr;
   bool is_function_var_in_context =
       function != nullptr && function->IsContextSlot();
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS -
          (is_function_var_in_context ? 1 : 0);
 }
 
 }  // namespace internal
 }  // namespace v8