Add summary support for ShowElementCombinator.end and .offset.

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

Index: pkg/analyzer/test/src/summary/resynthesize_test.dart
diff --git a/pkg/analyzer/test/src/summary/resynthesize_test.dart b/pkg/analyzer/test/src/summary/resynthesize_test.dart
index 30ae9fea77be75bf35915d5517e40ca420565ae9..5cacd04799697176244edf9821e2d228efa65afe 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_test.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_test.dart
@@ -745,6 +745,8 @@ class ResynthTest extends ResolverTestCase {
     if (original is ShowElementCombinatorImpl &&
         resynthesized is ShowElementCombinatorImpl) {
       expect(resynthesized.shownNames, original.shownNames);
+      expect(resynthesized.offset, original.offset);
+      expect(resynthesized.end, original.end);
     } else if (original is HideElementCombinatorImpl &&
         resynthesized is HideElementCombinatorImpl) {
       expect(resynthesized.hiddenNames, original.hiddenNames);