[fullcode][mips][mips64][ppc][s390] Avoid trashing of a home object when doing a count operation wi…

test/mjsunit/regress/regress-crbug-631917.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.
+
+var v = {};
+(function() {
+  var obj1 = { [v]: 42 };
+  var obj2 = {
+    testCounts() {
+      super[v]++;
+      return this[v];
+    }
+  }
+  Object.setPrototypeOf(obj2, obj1);
+  obj2.testCounts();
+
+  assertEquals(43, obj2.testCounts());
+  assertEquals(42, obj1[v]);
+}());