There are only 2 language modes, not 3

src/ast/scopes.h

 // 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.
 
 #ifndef V8_AST_SCOPES_H_
 #define V8_AST_SCOPES_H_
 
 #include "src/ast/ast.h"
 #include "src/base/hashmap.h"
 #include "src/globals.h"
@@ skipping 470 matching lines @@
   int num_stack_slots_;
   int num_heap_slots_;
   int num_global_slots_;
 
   // The scope type.
   const ScopeType scope_type_;
 
   // Scope-specific information computed during parsing.
   //
   // The language mode of this scope.
-  STATIC_ASSERT(LANGUAGE_END == 3);
-  LanguageMode language_mode_ : 2;
+  STATIC_ASSERT(LANGUAGE_END == 2);
+  LanguageMode language_mode_ : 1;
   // This scope is inside a 'with' of some outer scope.
   bool scope_inside_with_ : 1;
   // This scope or a nested catch scope or with scope contain an 'eval' call. At
   // the 'eval' call site this scope is the declaration scope.
   bool scope_calls_eval_ : 1;
   // This scope uses "super" property ('super.foo').
   bool scope_uses_super_property_ : 1;
   // This scope has a parameter called "arguments".
   bool has_arguments_parameter_ : 1;
   // This scope contains an "use asm" annotation.
@@ skipping 380 matching lines @@
   // Convenience variable; Subclass constructor only
   Variable* this_function_;
   // Module descriptor; module scopes only.
   ModuleDescriptor* module_descriptor_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_SCOPES_H_