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

test/mjsunit/regress/readonly3.js

Index: test/mjsunit/regress/readonly3.js
diff --git a/test/mjsunit/regress/regress-2565.js b/test/mjsunit/regress/readonly3.js
similarity index 74%
copy from test/mjsunit/regress/regress-2565.js
copy to test/mjsunit/regress/readonly3.js
index a77806a62e2209d355fce393b98797f1d20f40f8..dc71daac4c552b8e0446c189cd9c3b19de9f94f7 100644
--- a/test/mjsunit/regress/regress-2565.js
+++ b/test/mjsunit/regress/readonly3.js
@@ -25,8 +25,41 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-Object.freeze(Object.prototype);
+this.x = 0;
+
 var p = {};
-var o = Object.create(p);
-assertSame(p, o.__proto__);
-assertSame(p, Object.getPrototypeOf(o));
+Object.defineProperty(p, "x", {writable:false, value:5});
+this.__proto__ = p;
+
+function s(v) {
+  v.x = 1;
+}
+
+function s_strict(v) {
+  "use strict";
+  v.x = 1;
+}
+
+function c(p) {
+  return {__proto__: p};
+}
+
+var o1 = c(this);
+var o2 = c(this);
+
+// Initialize the store IC.
+s(c(this));
+s(c(this));
+s_strict(c(this));
+s_strict(c(this));
+
+delete this.x;
+
+// 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);
+assertThrows("s_strict(o2);");