Add summary support for ShowElementCombinator.end and .offset.

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 40c9a9b2e9619fa3c8b1f5cc195c959ebd0152a1..b702630a3d3a658d1960f32583c3bf8dd9ccc8f9 100644
--- a/pkg/analyzer/lib/src/summary/resynthesize.dart
+++ b/pkg/analyzer/lib/src/summary/resynthesize.dart
@@ -1019,6 +1019,8 @@ class _LibraryResynthesizer {
       // Note: we call toList() so that we don't retain a reference to the
       // deserialized data structure.
       combinator.shownNames = serializedCombinator.shows.toList();
+      combinator.offset = serializedCombinator.offset;
+      combinator.end = serializedCombinator.end;
       return combinator;
     } else {
       HideElementCombinatorImpl combinator = new HideElementCombinatorImpl();