Use regular map-checks to guard string-length loading.

src/code-stubs.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 812 matching lines @@
   explicit FunctionPrototypeStub(Code::Kind kind) : ICStub(kind) { }
   virtual void Generate(MacroAssembler* masm);
 
  private:
   virtual CodeStub::Major MajorKey() { return FunctionPrototype; }
 };
 
 
 class StringLengthStub: public ICStub {
  public:
-  StringLengthStub(Code::Kind kind, bool support_wrapper)
-      : ICStub(kind), support_wrapper_(support_wrapper) { }
+  explicit StringLengthStub(Code::Kind kind) : ICStub(kind) { }
   virtual void Generate(MacroAssembler* masm);
 
  private:
   STATIC_ASSERT(KindBits::kSize == 4);
-  class WrapperModeBits: public BitField<bool, 4, 1> {};
-  virtual CodeStub::Major MajorKey() { return StringLength; }
-  virtual int MinorKey() {
-    return KindBits::encode(kind()) | WrapperModeBits::encode(support_wrapper_);
-  }
-
-  bool support_wrapper_;
+    virtual CodeStub::Major MajorKey() { return StringLength; }
 };
 
 
 class StoreICStub: public ICStub {
  public:
   StoreICStub(Code::Kind kind, StrictModeFlag strict_mode)
       : ICStub(kind), strict_mode_(strict_mode) { }
 
  protected:
   virtual Code::ExtraICState GetExtraICState() {
@@ skipping 1451 matching lines @@
   int MinorKey() { return 0; }
 
   void Generate(MacroAssembler* masm);
 
   DISALLOW_COPY_AND_ASSIGN(ProfileEntryHookStub);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CODE_STUBS_H_