Fix failure to get source maps on windows with base change in index.html (#1625)

* Fix failure to get source maps on windows with base change

* Updated changelog

* Fix test failures

Author: Anna Gringauze

dwds/CHANGELOG.md

@@ -2,6 +2,7 @@
 - Make data types null safe
 - Update `package:vm_service` to 8.3.0.
 - Convert JavaScript stack traces in uncaught exceptions to Dart stack traces.
+- Fix failure to set breakpoints on windows with a base change in index.html.
 
 ## 14.0.2
 - Update the min SDK constraint to 2.17.0.

dwds/lib/src/loaders/frontend_server_require.dart

@@ -37,7 +37,10 @@ class FrontendServerRequireStrategyProvider {
   String _removeBasePath(String path) =>
       path.startsWith(_basePath) ? path.substring(_basePath.length) : null;
 
-  String _addBasePath(String serverPath) => p.join(_basePath, serverPath);
+  String _addBasePath(String serverPath) =>
+      _basePath == null || _basePath.isEmpty
+          ? relativizePath(serverPath)
+          : '$_basePath/${relativizePath(serverPath)}';
 
   Future<Map<String, String>> _moduleProvider(
           MetadataProvider metadataProvider) async =>
@@ -55,14 +58,12 @@ class FrontendServerRequireStrategyProvider {
       _addBasePath((await metadataProvider.moduleToModulePath)[module] ?? '');
 
   Future<String> _sourceMapPathForModule(
-      MetadataProvider metadataProvider, String module) async {
-    var path = (await metadataProvider.moduleToSourceMap)[module] ?? '';
-    return _addBasePath(relativizePath(path));
-  }
+          MetadataProvider metadataProvider, String module) async =>
+      _addBasePath((await metadataProvider.moduleToSourceMap)[module] ?? '');
 
   String _serverPathForAppUri(String appUri) {
     if (appUri.startsWith('org-dartlang-app:')) {
-      return _addBasePath(Uri.parse(appUri).path.substring(1));
+      return _addBasePath(Uri.parse(appUri).path);
     }
     return null;
   }