[turbofan] Simply context specialization and fix for OSR.

test/mjsunit/compiler/osr-block-scope-func.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
 
 "use strict";
 
 function foo() {
   var result;
   {
     let sum = 0;
     for (var i = 0; i < 100; i++) {
       if (i == 50) %OptimizeOsr();
       sum += i;
     }
     result = ret;
     function ret() {
       return sum;
     }
   }
   return result;
 }
 
 assertEquals(4950, foo()());
 assertEquals(4950, foo()());
 assertEquals(4950, foo()());
-
-function bar() {
-  var result;
-  {
-    let sum = 0;
-    for (let i = 0; i < 90; i++) {
-      sum += i;
-      if (i == 45) %OptimizeOsr();
-    }
-    result = ret;
-    function ret() {
-      return sum;
-    }
-  }
-  return result;
-}
-
-assertEquals(4005, bar()());
-assertEquals(4005, bar()());
-assertEquals(4005, bar()());