Remove deprecated string features.

tests/corelib/string_fromcharcode_test.dart

+// Copyright (c) 2012, 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.
+
+main() {
+  Expect.equals("A", new String.fromCharCode(65));
+  Expect.equals("B", new String.fromCharCode(66));
+  var gClef = new String.fromCharCode(0x1D11E);
+  Expect.equals(2, gClef.length);
+  Expect.equals(0xD834, gClef.codeUnitAt(0));
+  Expect.equals(0xDD1E, gClef.codeUnitAt(1));
+
+  // Unmatched surrogates.
+  var unmatched = new String.fromCharCode(0xD800);
+  Expect.equals(1, unmatched.length);
+  Expect.equals(0xD800, unmatched.codeUnitAt(0));
+  unmatched = new String.fromCharCode(0xDC00);
+  Expect.equals(1, unmatched.length);
+  Expect.equals(0xDC00, unmatched.codeUnitAt(0));
+
+  Expect.throws(() => new String.fromCharCode(-1),
+                (e) => e is ArgumentError);
+
+  // Invalid code point.
+  Expect.throws(() => new String.fromCharCode(0x110000),
+                (e) => e is ArgumentError);
+
+  Expect.throws(() => new String.fromCharCode(0x110001),
+                (e) => e is ArgumentError);
+}