[crankshaft] FIx for in deopt at the end of the loop.

test/mjsunit/regress/regress-662904.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --allow-natives-syntax
 
 function foo(a) {
-  for (var d in a) {
-    delete a[1];
+  var sum = 0;
+  var a = [0, "a"];
+  for (var i in a) {
+    sum += a[i];
   }
+  return sum;
 }
 
-foo([1,2,3]);
-foo([2,3,4]);
+assertEquals("0a", foo());
+assertEquals("0a", foo());
 %OptimizeFunctionOnNextCall(foo);
-foo([1,2,3]);
-assertOptimized(foo);
+assertEquals("0a", foo());