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

test/mjsunit/regress/setter.js

Index: test/mjsunit/regress/setter.js
diff --git a/test/mjsunit/regress/regress-2565.js b/test/mjsunit/regress/setter.js
similarity index 73%
copy from test/mjsunit/regress/regress-2565.js
copy to test/mjsunit/regress/setter.js
index a77806a62e2209d355fce393b98797f1d20f40f8..e3a8000f2bc55c9ee09c483a1cc421305415b85d 100644
--- a/test/mjsunit/regress/regress-2565.js
+++ b/test/mjsunit/regress/setter.js
@@ -25,8 +25,42 @@
 // (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);
+function s(v) {
+  v.x = 1;
+}
+
+function c(p) {
+  return {__proto__: p};
+}
+
 var p = {};
-var o = Object.create(p);
-assertSame(p, o.__proto__);
-assertSame(p, Object.getPrototypeOf(o));
+
+var o1 = c(p);
+var o2 = c(p);
+var o3 = c(p);
+var o4 = c(p);
+var o5 = c(p);
+
+// Initialize the store IC.
+s(o1);
+s(o2);
+
+// Install a setter on p.x
+var count = 0;
+Object.defineProperty(p, "x", {
+  set: function(x) {
+    count += 1;
+  }
+});
+
+// Verify that the setter was called directly.
+o3.x = 20;
+assertEquals(1, count);
+
+// Verify that monomorphic prototype failure is triggered in the IC.
+s(o4);
+assertEquals(2, count);
+
+// Verify that the newly installed IC is correct.
+s(o5);
+assertEquals(3, count);