Remove dart:platform library.

tests/lib/platform/uri_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";
-import "dart:platform" as platform;
-
-main() {
-  if (platform.operatingSystem == 'windows') {
-    Expect.equals("a\\b", Uri.parse("a/b").toFilePath());
-    Expect.equals("a\\b\\", Uri.parse("a/b/").toFilePath());
-    Expect.equals("a b", Uri.parse("a%20b").toFilePath());
-    Expect.equals("\\a b", Uri.parse("file:///a%20b").toFilePath());
-    Expect.equals("\\a\\b", Uri.parse("file:///a/b").toFilePath());
-    Expect.equals("C:\\", Uri.parse("file:///C:").toFilePath());
-    Expect.equals("C:\\", Uri.parse("file:///C:/").toFilePath());
-    Expect.equals("\\\\host\\a\\b", Uri.parse("file://host/a/b").toFilePath());
-
-    Expect.equals("a\\b", new Uri.file("a/b").toFilePath());
-    Expect.equals("a\\b", new Uri.file("a\\b").toFilePath());
-    Expect.equals("\\a\\b", new Uri.file("/a/b").toFilePath());
-    Expect.equals("\\a\\b", new Uri.file("\\a\\b").toFilePath());
-    Expect.equals("\\a\\b", new Uri.file("\\a/b").toFilePath());
-    Expect.equals("\\a\\b", new Uri.file("/a\\b").toFilePath());
-  } else {
-    Expect.equals("a/b", Uri.parse("a/b").toFilePath());
-    Expect.equals("a/b/", Uri.parse("a/b/").toFilePath());
-    Expect.equals("a b", Uri.parse("a%20b").toFilePath());
-    Expect.equals("/a b", Uri.parse("file:///a%20b").toFilePath());
-    Expect.equals("/a/b", Uri.parse("file:///a/b").toFilePath());
-    Expect.equals("/C:", Uri.parse("file:///C:").toFilePath());
-    Expect.equals("/C:/", Uri.parse("file:///C:/").toFilePath());
-    Expect.throws(() => Uri.parse("file://host/a/b").toFilePath(),
-                  (e) => e is UnsupportedError);
-
-    Expect.equals("a/b", new Uri.file("a/b").toFilePath());
-    Expect.equals("a\\b", new Uri.file("a\\b").toFilePath());
-  }
-}