A64: Synchronize with r15545.

test/webkit/cyclic-prototypes.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
 //
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 // modification, are permitted provided that the following conditions
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 // SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-description(
-"Tests the behavior of Array.prototype.concat while the array is having a bad time due to one of the elements we are concatenating."
-);
+description("This test makes sure we don't hang when setting cyclic prototype values: http://bugs.webkit.org/show_bug.cgi?id=6985")
 
-Object.defineProperty(Array.prototype, 0, { writable: false });
-shouldBe("[42].concat()", "[42]");
+var o1 = { p1: 1 };
+var o2 = { p2: 2 };
+o2.__proto__ = o1;
+var o3 = { p3: 3 };
+o3.__proto__ = o2;
 
+// Try to create a cyclical prototype chain.
+shouldThrow("o1.__proto__ = o3;");
 
+// This changes behaviour, since __proto__ is an accessor on Object.prototype.
+o1.__proto__ = null;
+
+shouldBeFalse("({}).hasOwnProperty.call(o1, '__proto__')");
+o1.__proto__ = o3;
+shouldBeTrue("({}).hasOwnProperty.call(o1, '__proto__')");
+shouldBe("Object.getPrototypeOf(o1)", "null");