Use a different map to distinguish eval contexts

test/mjsunit/regress/regress-5295-2.js

+// Copyright 2016 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: --test-small-max-function-context-stub-size
+
+// Generate an eval scope with a very large closure.
+// Ensure that vars are leaked out properly in this case.
+source = "var x;";
+for (var i = 0; i < 11; i++) {
+  source += "  let a_" + i + " = 0;\n";
+}
+source += "  (function () {\n"
+for (var i = 0; i < 11; i++) {
+  source += "a_" + i + "++;\n";
+}
+source += "})();\n"
+
+eval(source);
+assertEquals(undefined, x);