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

test/mjsunit/compiler/osr-backedges1.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 foo(a) {
+  var i = a | 0;
+  while (true) {
+    if (i == 0) { i = 1; continue; }
+    if (i == 1) { i = 2; continue; }
+    if (i == 2) { i = 3; continue; }
+    if (i == 3) { i = 4; continue; }
+    if (i == 4) { i = 5; continue; }
+    if (i == 5) { i = 6; continue; }
+    if (i == 6) { i = 7; continue; }
+    if (i == 7) { i = 8; continue; }
+    for (var j = 0; j < 10; j++) { if (i == 5) %OptimizeOsr(); }
+    break;
+  }
+  return j;
+}
+
+function test(func, tv, fv) {
+  assertEquals(tv, func(0));
+  assertEquals(tv, func(0));
+  assertEquals(fv, func(9));
+  assertEquals(fv, func(9));
+}
+
+test(foo, 10, 10);