Fix DDC errors on DDC

lib/src/dependency_graph.dart

Index: lib/src/dependency_graph.dart
diff --git a/lib/src/dependency_graph.dart b/lib/src/dependency_graph.dart
index 14dda6285276b43b7cce56f621cb61943caf6fbf..96e4bfaf208f464299eb8745c272c1842baa2e07 100644
--- a/lib/src/dependency_graph.dart
+++ b/lib/src/dependency_graph.dart
@@ -17,7 +17,8 @@ import 'package:analyzer/src/generated/ast.dart'
         ImportDirective,
         LibraryDirective,
         PartDirective,
-        PartOfDirective;
+        PartOfDirective,
+        UriBasedDirective;
 import 'package:analyzer/src/generated/engine.dart'
     show ParseDartTask, AnalysisContext;
 import 'package:analyzer/src/generated/source.dart' show Source, SourceKind;
@@ -279,11 +280,13 @@ class DartSourceNode extends SourceNode {
         if (d is PartOfDirective) return;
         if (d is LibraryDirective) continue;
 
+        var directiveUri = (d as UriBasedDirective).uri;
+
         // `dart:core` and other similar URLs only contain a name, but it is
         // meant to be a folder when resolving relative paths from it.
         var targetUri = uri.scheme == 'dart' && uri.pathSegments.length == 1
-            ? Uri.parse('$uri/').resolve(d.uri.stringValue)
-            : uri.resolve(d.uri.stringValue);
+            ? Uri.parse('$uri/').resolve(directiveUri.stringValue)
+            : uri.resolve(directiveUri.stringValue);
         var target =
             ParseDartTask.resolveDirective(graph._context, _source, d, null);
         if (target != null) {