Add corelib tests

test/codegen/corelib/string_source_test.dart

+// Copyright (c) 2013, 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.
+
+// Test that different representations of the same string are all equal.
+
+import "dart:convert";
+
+import "package:expect/expect.dart";
+
+main() {
+  var base = "\u{10412}";
+  var strings = [
+    "\u{10412}",
+    "𐐒",
+    new String.fromCharCodes([0xd801, 0xdc12]),
+    base[0] + base[1],
+    "$base",
+    "${base[0]}${base[1]}",
+    "${base[0]}${base.substring(1)}",
+    new String.fromCharCodes([0x10412]),
+    ("a" + base).substring(1),
+    (new StringBuffer()..writeCharCode(0xd801)
+                       ..writeCharCode(0xdc12)).toString(),
+    (new StringBuffer()..writeCharCode(0x10412)).toString(),
+    JSON.decode('"\u{10412}"'),
+    (JSON.decode('{"\u{10412}":[]}') as Map).keys.first
+  ];
+  for (String string in strings) {
+    Expect.equals(base.length, string.length);
+    Expect.equals(base, string);
+    Expect.equals(base.hashCode, string.hashCode);
+    Expect.listEquals(base.codeUnits.toList(), string.codeUnits.toList());
+  }
+}