Make it easier to test OSR with %OptimizeOsr() runtime call.

test/mjsunit/compiler/osr-top3.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --use-osr --allow-natives-syntax
+
+for (var k = 0; k < 2; k++) {
+  for (var j = 0; j < 3; j++) {
+    var sum = 0;
+    for (var i = 0; i < 1000; i++) {
+      if (i == 100) %OptimizeOsr();
+      var x = i + 2;
+      var y = x + 5;
+      var z = y + 3;
+      sum += z;
+    }
+    assertEquals(509500, sum);
+  }
+  assertEquals(509500, sum);
+}
+
+assertEquals(509500, sum);