Resolve URIs of parts of imported libraries relative to importing library sources.

pkg/analyzer/lib/src/summary/resynthesize.dart

Index: pkg/analyzer/lib/src/summary/resynthesize.dart
diff --git a/pkg/analyzer/lib/src/summary/resynthesize.dart b/pkg/analyzer/lib/src/summary/resynthesize.dart
index 891300e27ede08d486603db82654905a0029b383..15b712d6eb7ecd5cd47051c360eece0de799eb98 100644
--- a/pkg/analyzer/lib/src/summary/resynthesize.dart
+++ b/pkg/analyzer/lib/src/summary/resynthesize.dart
@@ -1252,8 +1252,8 @@ class _LibraryResynthesizer {
     String partUri;
     if (unit != 0) {
       String uri = dependency.parts[unit - 1];
-      Source partSource = summaryResynthesizer.sourceFactory
-          .resolveUri(referencedLibrarySource, uri);
+      Source partSource =
+          summaryResynthesizer.sourceFactory.resolveUri(librarySource, uri);
       partUri = partSource.uri.toString();
     } else {
       partUri = referencedLibraryUri;