Use absolute URIs for LinkedDependency.uri/parts.

pkg/analyzer/test/src/summary/summarize_ast_test.dart

Index: pkg/analyzer/test/src/summary/summarize_ast_test.dart
diff --git a/pkg/analyzer/test/src/summary/summarize_ast_test.dart b/pkg/analyzer/test/src/summary/summarize_ast_test.dart
index 4105d3224f29e934937fcfc03d2b9a7752324231..11e7156d465369fa42e35e147281357278791e52 100644
--- a/pkg/analyzer/test/src/summary/summarize_ast_test.dart
+++ b/pkg/analyzer/test/src/summary/summarize_ast_test.dart
@@ -224,6 +224,9 @@ class LinkerInputs {
   }
 
   UnlinkedUnit getUnit(String absoluteUri) {
+    if (absoluteUri == null) {
+      return null;
+    }
     UnlinkedUnit unit = _uriToUnit[absoluteUri] ??
         SerializedMockSdk.instance.uriToUnlinkedUnit[absoluteUri] ??
         _dependentUnlinkedUnits[absoluteUri];