Avoid setting transitions in-place for cached maps when observed

test/mjsunit/regress/regress-observe-map-cache.js

Index: test/mjsunit/regress/regress-observe-map-cache.js
diff --git a/test/mjsunit/regress/regress-store-global-proxy.js b/test/mjsunit/regress/regress-observe-map-cache.js
similarity index 58%
copy from test/mjsunit/regress/regress-store-global-proxy.js
copy to test/mjsunit/regress/regress-observe-map-cache.js
index c85531c5fd917daa67b54e87141a164b90f3729b..4c7a7e3e973d12cde43caaa64b11f6f08cef3dcc 100644
--- a/test/mjsunit/regress/regress-store-global-proxy.js
+++ b/test/mjsunit/regress/regress-observe-map-cache.js
@@ -2,11 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-delete Object.prototype.__proto__;
+// Flags: --allow-natives-syntax --enable-slow-asserts
 
 function f() {
-  this.toString = 1;
+  var x = new Array(0);
+  x[-1] = -1;
+  Object.observe(x, function() { });
 }
 
-f.apply({});
+f();
 f();