[turbofan] Rename context stack as part of the environment for OSR.

test/mjsunit/compiler/osr-block-scope-id.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 = new Array();
+  var out;
+  {
+    let sum = 0;
+    for (var i = 0; i < 10; i++) {
+      {
+        let x = i;
+        if (i == 5) %OptimizeOsr();
+        sum += i;
+        result.push(function() { return x; });
+      }
+    }
+    out = sum;
+  }
+  result.push(out);
+  return result;
+}
+
+
+function check() {
+  var r = foo();
+  assertEquals(45, r.pop());
+  for (var i = 9; i >= 0; i--) {
+    assertEquals(i, r.pop()());
+  }
+  assertEquals(0, r.length);
+}
+
+check();
+check();
+check();