Update URI related documentation and examples.

tests/corelib/uri_file_test.dart

Index: tests/corelib/uri_file_test.dart
diff --git a/tests/corelib/uri_file_test.dart b/tests/corelib/uri_file_test.dart
index 79da8335d45a955cd34a54af594c54ee9a1299e5..ab7c6ab573032d3eb056abf5e41df7e59f19b52d 100644
--- a/tests/corelib/uri_file_test.dart
+++ b/tests/corelib/uri_file_test.dart
@@ -88,6 +88,8 @@ testFileUriWindowsSlash() {
     ["file:///C:/", "C:/", "C:\\"],
     ["file:///C:/a/b", "C:/a/b", "C:\\a\\b"],
     ["file:///C:/a/b/", "C:/a/b/", "C:\\a\\b\\"],
+
+    ["file:///C:/xxx/yyy", "C:\\xxx\\yyy", "C:\\xxx\\yyy"],
   ];
 
   for (var test in tests) {