[web] Use 'Uri' instead of 'dart:html' to extract pathname (#127983)

- Use `Uri.parse()` to extract pathname.
- Remove unused code from `utils.dart`.
- Add test for URL encoding.

(need to wait for https://github.com/flutter/flutter/pull/126851 to make it into Google3)

packages/flutter_web_plugins/lib/src/navigation/utils.dart

@@ -2,28 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:html';
-
-final AnchorElement _urlParsingNode = AnchorElement();
-
 /// Extracts the pathname part of a full [url].
 ///
 /// Example: for the url `http://example.com/foo`, the extracted pathname will
 /// be `/foo`.
 String extractPathname(String url) {
-  _urlParsingNode.href = url; // ignore: unsafe_html, node is never exposed to the user
-  final String pathname = _urlParsingNode.pathname ?? '';
-  return (pathname.isEmpty || pathname[0] == '/') ? pathname : '/$pathname';
+  return ensureLeadingSlash(Uri.parse(url).path);
 }
 
-// The <base> element in the document.
-final Element? _baseElement = document.querySelector('base');
-
-/// Returns the `href` attribute of the <base> element in the document.
-///
-/// Returns null if the element isn't found.
-String? getBaseElementHrefFromDom() => _baseElement?.getAttribute('href');
-
 /// Checks that [baseHref] is set.
 ///
 /// Throws an exception otherwise.

packages/flutter_web_plugins/pubspec.yaml

@@ -9,10 +9,9 @@ dependencies:
   flutter:
     sdk: flutter
 
-  js: 0.6.7
-
   characters: 1.3.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   collection: 1.17.2 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
+  js: 0.6.7 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   material_color_utilities: 0.5.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   meta: 1.9.1 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   vector_math: 2.1.4 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"

packages/flutter_web_plugins/test/navigation/utils_test.dart

@@ -33,5 +33,9 @@ void main() {
     expect(extractPathname('https://example.com/foo'), '/foo');
     expect(extractPathname('https://example.com/foo#bar'), '/foo');
     expect(extractPathname('https://example.com/foo/#bar'), '/foo/');
+
+    // URL encoding.
+    expect(extractPathname('/foo bar'), '/foo%20bar');
+    expect(extractPathname('https://example.com/foo bar'), '/foo%20bar');
   });
 }