Fixing string compile-time constant evaluation

tests/language/src/ConstStringTest.dart

+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Exercises compile-time string constants
+
+main() {
+  // Constant comparisons are independent of the quotes used.
+  Expect.isTrue("abcd" === 'abcd');
+  Expect.isTrue('abcd' === "abcd");
+  Expect.isTrue("ab\"cd" === 'ab"cd');
+  Expect.isTrue('ab\'cd' === "ab'cd");
+
+  // String concatenation works even when quotes are different.
+  Expect.isTrue("abcd" === "ab" + "cd");
+  Expect.isTrue("abcd" === "ab" + 'cd');
+  Expect.isTrue("abcd" === 'ab' + 'cd');
+  Expect.isTrue("abcd" === 'ab' + "cd");
+
+  // Or when there are more than 2 contatenations.
+  Expect.isTrue("abcd" === "a" + "b" + "cd");
+  Expect.isTrue("abcd" === "a" + "b" + "c" + "d");
+  Expect.isTrue('abcd' === 'a' + 'b' + 'c' + 'd');
+  Expect.isTrue("abcd" === "a" + "b" + 'c' + "d");
+  Expect.isTrue("abcd" === 'a' + 'b' + 'c' + 'd');
+  Expect.isTrue("abcd" === 'a' + "b" + 'c' + "d");
+
+  Expect.isTrue("a'b'cd" === "a" + "'b'" + 'c' + "d");
+  Expect.isTrue("a\"b\"cd" === "a" + '"b"' + 'c' + "d");
+  Expect.isTrue("a\"b\"cd" === "a" + '"b"' + 'c' + "d");
+  Expect.isTrue("a'b'cd" === 'a' + "'b'" + 'c' + "d");
+  Expect.isTrue('a\'b\'cd' === "a" + "'b'" + 'c' + "d");
+  Expect.isTrue("a\"b\"cd" === 'a' + '"b"' + 'c' + "d");
+}