harmony-scoping: better error messages for let declarations in sloppy mode.

test/mjsunit/harmony/block-non-strict-errors.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.
+
+// Flags: --harmony-scoping
+
+function CheckError(source) {
+  var exception = null;
+  try {
+    eval(source);
+  } catch (e) {
+    exception = e;
+  }
+  assertNotNull(exception);
+  assertEquals(
+      "Lexical declarations are currently only allowed in strict mode",
+      exception.message);
+}
+
+
+function CheckOk(source) {
+  eval(source);
+}
+
+CheckError("let x = 1;");
+CheckError("{ let x = 1; }");
+CheckError("function f() { let x = 1; }");
+CheckError("for (let x = 1; x < 1; x++) {}");
+CheckError("for (let x of []) {}");
+CheckError("for (let x in []) {}");
+
+CheckOk("let = 1;");
+CheckOk("{ let = 1; }");
+CheckOk("function f() { let = 1; }");
+CheckOk("for (let = 1; let < 1; let++) {}");