Replace 'length' with more generic 'extractProperty' operation.

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/generated/utilities_dart.dart';
 import 'package:analyzer/src/summary/format.dart';
 import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/name_filter.dart';
 
 /**
@@ skipping 403 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.propertyAccessor) {
-            references
-                .add(new LinkedReferenceBuilder(kind: ReferenceKind.length));
-            continue;
-          }
-        }
-        // Anything prefixed with 'unresolved' is unresolved.
-        if (references[reference.prefixReference].kind ==
-            ReferenceKind.unresolved) {
-          namespace = const <String, _Meaning>{};
-        }
-        // Prefix references must always point to proper prefixes.
-        assert(namespace != null);
+        // Expressions like 'a.b.c.d' cannot be prelinked.
+        namespace ??= const <String, _Meaning>{};
       }
       _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;
         }
         references.add(meaning.encodeReference());
       } else {
@@ skipping 62 matching lines @@
    */
   String resolveUri(String sourceUri, String relativeUri) {
     if (sourceUri == null) {
       return relativeUri;
     } else {
       return resolveRelativeUri(Uri.parse(sourceUri), Uri.parse(relativeUri))
           .toString();
     }
   }
 }