[turbofan] Properly guard keyed stores wrt. setters in the prototype chain.

test/mjsunit/regress/regress-5275-2.js

Index: test/mjsunit/regress/regress-5275-2.js
diff --git a/test/mjsunit/regress/regress-5085.js b/test/mjsunit/regress/regress-5275-2.js
similarity index 53%
copy from test/mjsunit/regress/regress-5085.js
copy to test/mjsunit/regress/regress-5275-2.js
index 0ed034dc2d09e97827e2b4881570d60be2b5072b..2da422de9737b3358c52fce5a776b2df93e7afb2 100644
--- a/test/mjsunit/regress/regress-5085.js
+++ b/test/mjsunit/regress/regress-5275-2.js
@@ -5,10 +5,14 @@
 // Flags: --allow-natives-syntax
 
 function foo(x) {
-  return x instanceof Proxy;
+  var a = new Array(1);
+  a[0] = x;
+  return a;
 }
 
-assertFalse(foo({}));
-assertFalse(foo({}));
+assertEquals([1], foo(1));
+assertEquals([1], foo(1));
 %OptimizeFunctionOnNextCall(foo);
-assertFalse(foo({}));
+assertEquals([1], foo(1));
+Object.prototype.__defineSetter__("0", function() {});
+assertEquals([undefined], foo(1));