Overhaul the semantics of Request.handlerPath and Request.url.

test/shelf_io_test.dart

Index: test/shelf_io_test.dart
diff --git a/test/shelf_io_test.dart b/test/shelf_io_test.dart
index c1b4a410cd5fa9c5a0688de38d2a7f2b7dd8b5f1..ed82efd414e8072556bba78b576a65edef0ddd78 100644
--- a/test/shelf_io_test.dart
+++ b/test/shelf_io_test.dart
@@ -85,11 +85,11 @@ void main() {
       var expectedUrl = 'http://localhost:$_serverPort$path';
       expect(request.requestedUri, Uri.parse(expectedUrl));
 
-      expect(request.url.path, '/foo/bar');
+      expect(request.url.path, 'foo/bar');
       expect(request.url.pathSegments, ['foo', 'bar']);
       expect(request.protocolVersion, '1.1');
       expect(request.url.query, 'qs=value');
-      expect(request.scriptName, '');
+      expect(request.handlerPath, '/');
 
       return syncHandler(request);
     });