Change LookupForWrite to always do a full lookup and check the result.

test/mjsunit/regress/readonly2.js

 // Copyright 2013 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
 //       with the distribution.
 //     * Neither the name of Google Inc. nor the names of its
 //       contributors may be used to endorse or promote products derived
 //       from this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// Flags: --allow-natives-syntax
+Object.defineProperty(this, "x", { writable:true });
 
-"use strict";
-
-function f(a, b) {
-  return g("c", "d");
+function s(v) {
+  v.x = 1;
 }
 
-function g(a, b) {
-  g.constructor.apply(this, arguments);
+function c(p) {
+  var x = {};
+  x.__proto__ = p;
+  return x;
 }
 
-g.constructor = function(a, b) {
-  assertEquals("c", a);
-  assertEquals("d", b);
-}
+var o1 = c(this);
+var o2 = c(this);
 
-f("a", "b");
-f("a", "b");
-%OptimizeFunctionOnNextCall(f);
-f("a", "b");
-g.x = "deopt";
-f("a", "b");
+// Initialize the store IC.
+s(c(this));
+s(c(this));
+
+// Make x non-writable.
+Object.defineProperty(this, "x", { writable:false, value:5 });
+
+// Verify that direct setting fails.
+o1.x = 20;
+assertEquals(5, o1.x);
+
+// Verify that setting through the IC fails.
+s(o2);
+assertEquals(5, o2.x);