Attempt to fix DartEditBuilderImplTest on Windows.

pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart

Index: pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
diff --git a/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart b/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
index 5deadf51d3a448782e7a16764a5ad16e4042d1d2..608bc0b6ed0a7e6a201470a85f6cee9f29e85ee3 100644
--- a/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
+++ b/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
@@ -1365,7 +1365,8 @@ f(int i, String s) {
     DartChangeBuilderImpl builder = new DartChangeBuilderImpl(driver);
     await builder.addFileEdit(path, 1, (DartFileEditBuilder builder) {
       Iterable<_MockSource> sources = newUris.map((newUri) {
-        String path = newUri.contains(':') ? null : '/$newUri';
+        String path =
+            newUri.contains(':') ? null : provider.convertPath('/$newUri');
         return new _MockSource(path, Uri.parse(newUri));
       });
       builder.importLibraries(sources);