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

pkg/path/test/url_test.dart

Index: pkg/path/test/url_test.dart
diff --git a/pkg/path/test/url_test.dart b/pkg/path/test/url_test.dart
index e149b4f0e22dadb0795591860aedaa5781d73c41..58c7b929a6e235b1421504294c5b237b6dd95763 100644
--- a/pkg/path/test/url_test.dart
+++ b/pkg/path/test/url_test.dart
@@ -700,20 +700,28 @@ main() {
     expect(context.withoutExtension('a/b.c//'), 'a/b//');
   });
 
-  test('fromUri', () {
-    expect(context.fromUri(Uri.parse('http://dartlang.org/path/to/foo')),
-        'http://dartlang.org/path/to/foo');
-    expect(context.fromUri(Uri.parse('http://dartlang.org/path/to/foo/')),
-        'http://dartlang.org/path/to/foo/');
-    expect(context.fromUri(Uri.parse('file:///path/to/foo')),
-        'file:///path/to/foo');
-    expect(context.fromUri(Uri.parse('foo/bar')), 'foo/bar');
-    expect(context.fromUri(Uri.parse('http://dartlang.org/path/to/foo%23bar')),
-        'http://dartlang.org/path/to/foo%23bar');
-    // Since the resulting "path" is also a URL, special characters should
-    // remain percent-encoded in the result.
-    expect(context.fromUri(Uri.parse('_%7B_%7D_%60_%5E_%20_%22_%25_')),
-        r'_%7B_%7D_%60_%5E_%20_%22_%25_');
+  group('fromUri', () {
+    test('with a URI', () {
+      expect(context.fromUri(Uri.parse('http://dartlang.org/path/to/foo')),
+          'http://dartlang.org/path/to/foo');
+      expect(context.fromUri(Uri.parse('http://dartlang.org/path/to/foo/')),
+          'http://dartlang.org/path/to/foo/');
+      expect(context.fromUri(Uri.parse('file:///path/to/foo')),
+          'file:///path/to/foo');
+      expect(context.fromUri(Uri.parse('foo/bar')), 'foo/bar');
+      expect(context.fromUri(
+          Uri.parse('http://dartlang.org/path/to/foo%23bar')),
+          'http://dartlang.org/path/to/foo%23bar');
+      // Since the resulting "path" is also a URL, special characters should
+      // remain percent-encoded in the result.
+      expect(context.fromUri(Uri.parse('_%7B_%7D_%60_%5E_%20_%22_%25_')),
+          r'_%7B_%7D_%60_%5E_%20_%22_%25_');
+    });
+
+    test('with a string', () {
+      expect(context.fromUri('http://dartlang.org/path/to/foo'),
+          'http://dartlang.org/path/to/foo');
+    });
   });
 
   test('toUri', () {