Add regression test for optimized count operation.

test/mjsunit/regress/regress-crbug-306851.js

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 // Flags: --allow-natives-syntax
 
-var a = new Array(2);
-a[0] = 1;
-assertTrue(%HasFastSmiElements(a));
-assertTrue(%HasFastHoleyElements(a));
+function Counter() {
+  this.value = 0;
+};
 
-function hole(i) {
-  return a[i] << 0;
+Object.defineProperty(Counter.prototype, 'count', {
+  get: function() { return this.value; },
+  set: function(value) { this.value = value; }
+});
+
+var obj = new Counter();
+
+function bummer() {
+  obj.count++;
+  return obj.count;
 }
 
-assertEquals(1, hole(0));
-assertEquals(1, hole(0));
-%OptimizeFunctionOnNextCall(hole);
-assertEquals(0, hole(1));
+assertEquals(1, bummer());
+assertEquals(2, bummer());
+assertEquals(3, bummer());
+%OptimizeFunctionOnNextCall(bummer);
+assertEquals(4, bummer());
+assertEquals(5, bummer());
+assertEquals(6, bummer());