3.21 branch: Fix HObjectAccess for loads from migrating prototypes

test/mjsunit/regress/regress-crbug-305309.js

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 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // Flags: --allow-natives-syntax
 
-var do_set = false;
+function BadProto() {
+  this.constant_function = function() {};
+  this.one = 1;
+  this.two = 2;
+}
+var b1 = new BadProto();
+var b2 = new BadProto();
 
-%NeverOptimizeFunction(set_proto_elements);
-function set_proto_elements() {
-  if (do_set) Array.prototype[1] = 1.5;
+function Ctor() {}
+Ctor.prototype = b1;
+var a = new Ctor();
+
+function Two(x) {
+  return x.two;
 }
-
-function f(a, i) {
-  set_proto_elements();
-  return a[i] + 0.5;
-}
-
-var arr = [0.0,,2.5];
-assertEquals(0.5, f(arr, 0));
-assertEquals(0.5, f(arr, 0));
-%OptimizeFunctionOnNextCall(f);
-assertEquals(0.5, f(arr, 0));
-do_set = true;
-assertEquals(2, f(arr, 1));
-
+assertEquals(2, Two(a));
+assertEquals(2, Two(a));
+b2.constant_function = "no longer constant!";
+%OptimizeFunctionOnNextCall(Two);
+assertEquals(2, Two(a));