Allow [path.fromUri] to take a string as well as a URI.

pkg/path/lib/path.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.
 
 /// A comprehensive, cross-platform path manipulation library.
 ///
 /// ## Installing ##
 ///
 /// Use [pub][] to install this package. Add the following to your
 /// `pubspec.yaml` file.
@@ skipping 304 matching lines @@
 ///     path.isWithin('/root/path', '/root/path/a'); // -> true
 ///     path.isWithin('/root/path', '/root/other'); // -> false
 ///     path.isWithin('/root/path', '/root/path') // -> false
 bool isWithin(String parent, String child) => _context.isWithin(parent, child);
 
 /// Removes a trailing extension from the last part of [path].
 ///
 ///     withoutExtension('path/to/foo.dart'); // -> 'path/to/foo'
 String withoutExtension(String path) => _context.withoutExtension(path);
 
-/// Returns the path represented by [uri].
+/// Returns the path represented by [uri], which may be a [String] or a [Uri].
 ///
 /// For POSIX and Windows styles, [uri] must be a `file:` URI. For the URL
 /// style, this will just convert [uri] to a string.
 ///
 ///     // POSIX
-///     path.fromUri(Uri.parse('file:///path/to/foo'))
+///     context.fromUri('file:///path/to/foo')
 ///       // -> '/path/to/foo'
 ///
 ///     // Windows
-///     path.fromUri(Uri.parse('file:///C:/path/to/foo'))
+///     context.fromUri('file:///C:/path/to/foo')
 ///       // -> r'C:\path\to\foo'
 ///
 ///     // URL
-///     path.fromUri(Uri.parse('http://dartlang.org/path/to/foo'))
+///     context.fromUri('http://dartlang.org/path/to/foo')
 ///       // -> 'http://dartlang.org/path/to/foo'
-String fromUri(Uri uri) => _context.fromUri(uri);
+///
+/// If [uri] is relative, a relative path will be returned.
+///
+///     path.fromUri('path/to/foo'); // -> 'path/to/foo'
+String fromUri(uri) => _context.fromUri(uri);
 
 /// Returns the URI that represents [path].
 ///
 /// For POSIX and Windows styles, this will return a `file:` URI. For the URL
 /// style, this will just convert [path] to a [Uri].
 ///
 ///     // POSIX
 ///     path.toUri('/path/to/foo')
 ///       // -> Uri.parse('file:///path/to/foo')
 ///
 ///     // Windows
 ///     path.toUri(r'C:\path\to\foo')
 ///       // -> Uri.parse('file:///C:/path/to/foo')
 ///
 ///     // URL
 ///     path.toUri('http://dartlang.org/path/to/foo')
 ///       // -> Uri.parse('http://dartlang.org/path/to/foo')
 ///
 /// If [path] is relative, a relative URI will be returned.
 ///
 ///     path.toUri('path/to/foo')
 ///       // -> Uri.parse('path/to/foo')
 Uri toUri(String path) => _context.toUri(path);