Merge the dart:uri library into dart:core and update the Uri class

tests/corelib/uri_scheme_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.
+
+import "package:expect/expect.dart";
+
+void testInvalidArguments() {
+  Expect.throws(() => new Uri(scheme: "_"), (e) => e is ArgumentError);
+  Expect.throws(() => new Uri(scheme: "http_s"), (e) => e is ArgumentError);
+}
+
+void testScheme() {
+  test(String expectedScheme, String expectedUri, String scheme) {
+    var uri = new Uri(scheme: scheme);
+    Expect.equals(expectedScheme, uri.scheme);
+    Expect.equals(expectedUri, uri.toString());
+  }
+
+  test("http", "http:", "http");
+  test("http", "http:", "HTTP");
+  test("http+ssl", "http+ssl:", "HTTP+ssl");
+  test("urn", "urn:", "urn");
+  test("urn", "urn:", "UrN");
+}
+
+main() {
+  testInvalidArguments();
+  testScheme();
+}