Migrate client code to package:web (#3610)

* Recompile with latest Dart
* Increase constraint on package:web to avoid issues

pubspec.yaml

@@ -20,6 +20,7 @@ dependencies:
   path: ^1.8.3
   pub_semver: ^2.1.4
   source_span: ^1.10.0
+  web: ^0.5.1
   yaml: ^3.1.2
 
 dev_dependencies:

web/docs.dart

@@ -2,99 +2,14 @@
 // 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.
 
-import 'dart:html';
-
 import 'highlight.dart' as highlight;
 import 'search.dart' as search;
-import 'sidenav.dart' as sidenav;
+import 'sidebars.dart' as sidebars;
 import 'theme.dart' as theme;
-import 'web_interop.dart';
 
 void main() {
-  initializeSidebars();
+  sidebars.init();
   search.init();
-  sidenav.init();
   highlight.init();
   theme.init();
 }
-
-void initializeSidebars() {
-  final body = document.body;
-  if (body == null) {
-    return;
-  }
-  final dataUsingBaseHref = body.getAttribute('data-using-base-href');
-  if (dataUsingBaseHref == null) {
-    // This should never happen.
-    return;
-  }
-  final String baseHref;
-  if (dataUsingBaseHref != 'true') {
-    final dataBaseHref = body.getAttribute('data-base-href');
-    if (dataBaseHref == null) {
-      return;
-    }
-    baseHref = dataBaseHref;
-  } else {
-    baseHref = '';
-  }
-
-  final mainContent = document.getElementById('dartdoc-main-content');
-  if (mainContent == null) {
-    return;
-  }
-  final sanitizer = _SidebarNodeTreeSanitizer(baseHref);
-
-  void loadSidebar(String? sidebarPath, Element? sidebarElement) {
-    if (sidebarPath == null || sidebarPath.isEmpty || sidebarElement == null) {
-      return;
-    }
-
-    window.fetch('$baseHref$sidebarPath').then((response) async {
-      final fetchResponse = response as FetchResponse;
-      if (response.status != 200) {
-        final errorAnchor = (document.createElement('a') as AnchorElement)
-          ..href = 'https://dart.dev/tools/dart-doc#troubleshoot'
-          ..text = 'Failed to load sidebar. '
-              'Visit dart.dev for help troubleshooting.';
-        sidebarElement.append(errorAnchor);
-        return;
-      }
-
-      final content = await fetchResponse.text;
-
-      sidebarElement.setInnerHtml(content, treeSanitizer: sanitizer);
-    });
-  }
-
-  final aboveSidebarPath = mainContent.getAttribute('data-above-sidebar');
-  final leftSidebar = document.getElementById('dartdoc-sidebar-left-content');
-  loadSidebar(aboveSidebarPath, leftSidebar);
-
-  final belowSidebarPath = mainContent.getAttribute('data-below-sidebar');
-  final rightSidebar = document.getElementById('dartdoc-sidebar-right');
-  loadSidebar(belowSidebarPath, rightSidebar);
-}
-
-/// A permissive sanitizer that allows external links (e.g. to api.dart.dev) and
-/// adjusts the links in a newly loaded sidebar, if "base href" is not being
-/// used.
-class _SidebarNodeTreeSanitizer implements NodeTreeSanitizer {
-  final String baseHref;
-
-  _SidebarNodeTreeSanitizer(this.baseHref);
-
-  @override
-  void sanitizeTree(Node node) {
-    if (node is Element && node.nodeName == 'A') {
-      final hrefString = node.attributes['href'];
-      if (hrefString != null) {
-        final href = Uri.parse(hrefString);
-        if (!href.isAbsolute) {
-          node.setAttribute('href', '$baseHref$hrefString');
-        }
-      }
-    }
-    node.childNodes.forEach(sanitizeTree);
-  }
-}