Fix support for uri in part-of directive

pkg/analyzer/lib/src/dart/ast/ast.dart

Index: pkg/analyzer/lib/src/dart/ast/ast.dart
diff --git a/pkg/analyzer/lib/src/dart/ast/ast.dart b/pkg/analyzer/lib/src/dart/ast/ast.dart
index 398fa65acc662b5cf3091196609dda146792cfc1..656b1c2edf45728f52417a3e76b25d498819e789 100644
--- a/pkg/analyzer/lib/src/dart/ast/ast.dart
+++ b/pkg/analyzer/lib/src/dart/ast/ast.dart
@@ -8458,6 +8458,7 @@ class PartOfDirectiveImpl extends DirectiveImpl implements PartOfDirective {
   Iterable<SyntacticEntity> get childEntities => super._childEntities
     ..add(partKeyword)
     ..add(ofKeyword)
+    ..add(_uri)
     ..add(_libraryName)
     ..add(semicolon);