Improve 'length' instance property reference encoding.

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

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/src/summary/format.dart';
 import 'package:analyzer/src/summary/name_filter.dart';
 
 /**
  * Create a [LinkedLibraryBuilder] corresponding to the given
  * [definingUnit], which should be the defining compilation unit for a library.
@@ skipping 394 matching lines @@
     List<LinkedReferenceBuilder> references = <LinkedReferenceBuilder>[];
     for (int i = 0; i < unit.references.length; i++) {
       UnlinkedReference reference = unit.references[i];
       Map<String, _Meaning> namespace;
       if (reference.prefixReference == 0) {
         namespace = privateNamespace;
       } else {
         // Prefix references must always point backward.
         assert(reference.prefixReference < i);
         namespace = prefixNamespaces[reference.prefixReference];
+        // If in `a.length` the `a` prefix is a top-level variable or a field,
+        // then it must be the `String.length` property reference.
+        if (namespace == null && reference.name == 'length') {
+          ReferenceKind prefixKind = references[reference.prefixReference].kind;
+          if (prefixKind == ReferenceKind.topLevelPropertyAccessor ||
+              prefixKind == ReferenceKind.constField) {
+            references
+                .add(new LinkedReferenceBuilder(kind: ReferenceKind.length));
+            continue;
+          }
+        }
         // Prefix references must always point to proper prefixes.
         assert(namespace != null);
       }
       _Meaning meaning = namespace[reference.name];
       if (meaning != null) {
         if (meaning is _PrefixMeaning) {
           prefixNamespaces[i] = meaning.namespace;
         } else if (meaning is _ClassMeaning) {
           prefixNamespaces[i] = meaning.namespace;
         }
@@ skipping 63 matching lines @@
    * [sourceUri] is also relative.
    */
   String resolveUri(String sourceUri, String relativeUri) {
     if (sourceUri == null) {
       return relativeUri;
     } else {
       return Uri.parse(sourceUri).resolve(relativeUri).toString();
     }
   }
 }