Use shared function info for eval cache key.

test/mjsunit/regress/regress-eval-cache.js

+// Copyright 2014 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.
+
+(function f() {
+  try {
+    throw 1;
+  } catch (e) {
+    var a = 0;
+    var b = 0;
+    var c = 0;
+    var x = 1;
+    var result = eval('eval("x")').toString();
+    assertEquals("1", result);
+  }
+  var x = 2;
+  var result = eval('eval("x")').toString();
+  assertEquals("2", result);
+})();