IE 9 preventExtensions doesn't throw, even in strict mode.

test/object.js

@@ -212,11 +212,23 @@ describe('Object', function () {
 
       // Firefox 37 still has "pending exception" logic in its Object.assign implementation,
       // which is 72% slower than our shim, and Firefox 40's native implementation.
-      var thrower = Object.preventExtensions({ 1: 2 });
+      var thrower = Object.preventExtensions({ 1: 2, 2: 3, 3: 4 });
+      Object.defineProperty(thrower, 2, {
+        get: function () { return 3; },
+        set: function (v) { throw new RangeError('IE 9 does not throw on preventExtensions'); }
+      });
       var error;
-      try { Object.assign(thrower, 'xy'); } catch (e) { error = e; }
-      expect(error).to.be.an.instanceOf(TypeError);
-      expect(thrower).to.have.property(1, 2);
+      try { Object.assign(thrower, 'wxyz'); } catch (e) { error = e; }
+      expect(thrower).not.to.have.property(0);
+      if (thrower[1] === 'x') {
+        // IE 9 doesn't throw in strict mode with preventExtensions
+        expect(error).to.be.an.instanceOf(RangeError);
+      } else {
+        expect(error).to.be.an.instanceOf(TypeError);
+        expect(thrower).to.have.property(1, 2);
+      }
+      expect(thrower).to.have.property(2, 3);
+      expect(thrower).to.have.property(3, 4);
     });
 
     ifSymbolsIt('includes enumerable symbols, after keys', function () {