Allow inline caching for getting the length of string wrapper objects.

src/objects-inl.h

 // Copyright 2006-2008 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 283 matching lines @@
        SHARED_FUNCTION_INFO_TYPE);
 }
 
 
 bool Object::IsJSValue() {
   return Object::IsHeapObject()
     && HeapObject::cast(this)->map()->instance_type() == JS_VALUE_TYPE;
 }
 
 
+bool Object::IsStringWrapper() {
+  return IsJSValue() && JSValue::cast(this)->value()->IsString();
+}
+
+
 bool Object::IsProxy() {
   return Object::IsHeapObject()
     && HeapObject::cast(this)->map()->instance_type() == PROXY_TYPE;
 }
 
 
 bool Object::IsBoolean() {
   return IsTrue() || IsFalse();
 }
 
@@ skipping 2041 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_