Ensure locations are always provided, but don't store them yet.

pkg/front_end/lib/src/fasta/combinator.dart

Index: pkg/front_end/lib/src/fasta/combinator.dart
diff --git a/pkg/front_end/lib/src/fasta/combinator.dart b/pkg/front_end/lib/src/fasta/combinator.dart
index b2a5c36f7d383c5d51ca3e05e1e36e2a4814fc62..a0062c1b67117d87161aa2662fbbcbaedba150b9 100644
--- a/pkg/front_end/lib/src/fasta/combinator.dart
+++ b/pkg/front_end/lib/src/fasta/combinator.dart
@@ -9,13 +9,13 @@ class Combinator {
 
   final Set<String> names;
 
-  Combinator(this.isShow, this.names);
+  Combinator(this.isShow, this.names, int charOffset, Uri fileUri);
 
-  Combinator.show(Iterable <String> names)
-      : this(true, new Set<String>.from(names));
+  Combinator.show(Iterable <String> names, int charOffset, Uri fileUri)
+      : this(true, new Set<String>.from(names), charOffset, fileUri);
 
-  Combinator.hide(Iterable <String> names)
-      : this(false, new Set<String>.from(names));
+  Combinator.hide(Iterable <String> names, int charOffset, Uri fileUri)
+      : this(false, new Set<String>.from(names), charOffset, fileUri);
 
   bool get isHide => !isShow;
 }