Handle 'part of' declarations with URI correctly in Fasta.

pkg/front_end/lib/src/fasta/source/outline_builder.dart

Index: pkg/front_end/lib/src/fasta/source/outline_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/source/outline_builder.dart b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
index 15a24a74dbcfbb88fdd7f5bd612c226187aa11cd..3e4b7f152cd6af9d4dd8e2dae099c2f12218fde6 100644
--- a/pkg/front_end/lib/src/fasta/source/outline_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
@@ -576,11 +576,15 @@ class OutlineBuilder extends UnhandledListener {
   }
 
   @override
-  void endPartOf(Token partKeyword, Token semicolon) {
+  void endPartOf(Token partKeyword, Token semicolon, bool hasName) {
     debugEvent("endPartOf");
-    String name = pop();
+    String containingLibrary = pop();
     List<MetadataBuilder> metadata = pop();
-    library.addPartOf(metadata, name);
+    if (hasName) {
+      library.addPartOf(metadata, containingLibrary, null);
+    } else {
+      library.addPartOf(metadata, null, containingLibrary);
+    }
   }
 
   @override