Make visibleLength/visibleOffset 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 ba024afd8e7b5692b223e1396a96c9a5b4868778..07a946110587102f139ff1bfd80d244eb7938909 100644
--- a/pkg/analyzer/lib/src/summary/idl.dart
+++ b/pkg/analyzer/lib/src/summary/idl.dart
@@ -1926,12 +1926,14 @@ abstract class UnlinkedExecutable extends base.SummaryClass {
   /**
    * If a local function, the length of the visible range; zero otherwise.
    */
+  @informative
   @Id(20)
   int get visibleLength;
 
   /**
    * If a local function, the beginning of the visible range; zero otherwise.
    */
+  @informative
   @Id(21)
   int get visibleOffset;
 }