[turbofan] Use heavy-handed graph duplication to do loop peeling for OSR.

test/mjsunit/compiler/osr-nested2.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: --allow-natives-syntax --use-osr --turbo-osr
 
 function f() {
   var sum = 0;
   for (var i = 5; i < 6; i++) {
     for (var j = 0; j < 1000; j++) {
       var x = i + 2;
       var y = x + 5;
       var z = y + 3;
       sum += z;
       if (i == 21) %OptimizeOsr();
     }
-    if (true) break;
   }
   return sum;
 }
 
 
 assertEquals(15000, f());
 assertEquals(15000, f());
 assertEquals(15000, f());