[test] Add regression test for http://crbug.com/642056.

test/mjsunit/regress/regress-crbug-642056.js

Index: test/mjsunit/regress/regress-crbug-642056.js
diff --git a/test/mjsunit/compiler/regress-math-sign-nan-type.js b/test/mjsunit/regress/regress-crbug-642056.js
similarity index 71%
copy from test/mjsunit/compiler/regress-math-sign-nan-type.js
copy to test/mjsunit/regress/regress-crbug-642056.js
index e16eba8c5a3b8ca48f8a055579f6f42289f40a41..ca9fc78ef61bf58a6f0affa217632ccf171b9b19 100644
--- a/test/mjsunit/compiler/regress-math-sign-nan-type.js
+++ b/test/mjsunit/regress/regress-crbug-642056.js
@@ -4,11 +4,14 @@
 
 // Flags: --allow-natives-syntax
 
-function f(a) {
-  return Math.sign(+a) < 2;
+function f(o) {
+  return o.x instanceof Array;
 }
 
-f(NaN);
-f(NaN);
+var o = { x : 1.5 };
+o.x = 0;
+
+f(o);
+f(o);
 %OptimizeFunctionOnNextCall(f);
-assertFalse(f(NaN));
+f(o);