Clear 'referenceMap' before summarizing a new unit.

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

Index: pkg/analyzer/test/src/summary/summary_test.dart
diff --git a/pkg/analyzer/test/src/summary/summary_test.dart b/pkg/analyzer/test/src/summary/summary_test.dart
index 2fe16fa78ab643b1c07b4e2451e2da36705e107b..5b0ba9c47495e364a6f9e7177e20aed58e960aba 100644
--- a/pkg/analyzer/test/src/summary/summary_test.dart
+++ b/pkg/analyzer/test/src/summary/summary_test.dart
@@ -2003,15 +2003,14 @@ a.Stream s;
   }
 
   test_type_reference_to_part() {
-    addNamedSource('/a.dart', 'part of foo; class C {}');
-    checkTypeRef(
-        serializeTypeText('C',
-            otherDeclarations: 'library foo; part "a.dart";'),
-        null,
-        null,
-        'C',
+    addNamedSource('/a.dart', 'part of foo; class C { C(); }');
+    serializeLibraryText('library foo; part "a.dart"; C c;');
+    UnlinkedClass classA = findClass('C', unit: unlinkedUnits[1]);
+    checkTypeRef(classA.executables.single.returnType, null, null, 'C',
         expectedKind: PrelinkedReferenceKind.classOrEnum,
-        expectedTargetUnit: 1);
+        expectedTargetUnit: 1,
+        prelinkedSourceUnit: prelinked.units[1],
+        unlinkedSourceUnit: unlinkedUnits[1]);
   }
 
   test_type_reference_to_typedef() {