Mark some other instances of visibleLength/visibleOffset as informative.

pkg/analyzer/lib/src/summary/idl.dart

Index: pkg/analyzer/lib/src/summary/idl.dart
diff --git a/pkg/analyzer/lib/src/summary/idl.dart b/pkg/analyzer/lib/src/summary/idl.dart
index 07a946110587102f139ff1bfd80d244eb7938909..61f62a8bf0927583f21dacac30855441e1c85bbd 100644
--- a/pkg/analyzer/lib/src/summary/idl.dart
+++ b/pkg/analyzer/lib/src/summary/idl.dart
@@ -2337,12 +2337,14 @@ abstract class UnlinkedParam extends base.SummaryClass {
   /**
    * The length of the visible range.
    */
+  @informative
   @Id(10)
   int get visibleLength;
 
   /**
    * The beginning of the visible range.
    */
+  @informative
   @Id(11)
   int get visibleOffset;
 }
@@ -2818,12 +2820,14 @@ abstract class UnlinkedVariable extends base.SummaryClass {
   /**
    * If a local variable, the length of the visible range; zero otherwise.
    */
+  @informative
   @Id(11)
   int get visibleLength;
 
   /**
    * If a local variable, the beginning of the visible range; zero otherwise.
    */
+  @informative
   @Id(12)
   int get visibleOffset;
 }