Try again to fix the bots (TBR)

pkg/analyzer_plugin/test/support/abstract_context.dart

Index: pkg/analyzer_plugin/test/support/abstract_context.dart
diff --git a/pkg/analyzer_plugin/test/support/abstract_context.dart b/pkg/analyzer_plugin/test/support/abstract_context.dart
index 9ec849b040287c1955ad26fe10346b09a494ad18..216b07b13667f320fa81fbfeaeeec8946a4577e2 100644
--- a/pkg/analyzer_plugin/test/support/abstract_context.dart
+++ b/pkg/analyzer_plugin/test/support/abstract_context.dart
@@ -82,6 +82,9 @@ class Required {
   }
 
   Source addSource(String path, String content, [Uri uri]) {
+    if (path.startsWith('/')) {
+      path = provider.convertPath(path);
+    }
     driver.addFile(path);
     driver.changeFile(path);
     _fileContentOverlay[path] = content;