Improve 'length' instance property reference encoding.

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

Index: pkg/analyzer/lib/src/summary/summarize_const_expr.dart
diff --git a/pkg/analyzer/lib/src/summary/summarize_const_expr.dart b/pkg/analyzer/lib/src/summary/summarize_const_expr.dart
index 771dac90b84f242de15f7f772218944283e3528c..f6dea26583bf704a8ccfcb335aed436b62cdd1db 100644
--- a/pkg/analyzer/lib/src/summary/summarize_const_expr.dart
+++ b/pkg/analyzer/lib/src/summary/summarize_const_expr.dart
@@ -93,9 +93,8 @@ abstract class AbstractConstExprSerializer {
     } else if (expr is PrefixExpression) {
       _serializePrefixExpression(expr);
     } else if (expr is PropertyAccess) {
-      // TODO(scheglov) solve ambiguity of `a.b.length` where `a` and `b` are
-      // identifiers
-      if (expr.propertyName.name == 'length') {
+      if (expr.target is! PrefixedIdentifier &&
+          expr.propertyName.name == 'length') {
         serialize(expr.target);
         operations.add(UnlinkedConstOperation.length);
       } else {
@@ -110,6 +109,11 @@ abstract class AbstractConstExprSerializer {
   }
 
   /**
+   * Return [EntityRefBuilder] that corresponds to the given [constructor].
+   */
+  EntityRefBuilder serializeConstructorName(ConstructorName constructor);
+
+  /**
    * Return [EntityRefBuilder] that corresponds to the given [identifier].
    */
   EntityRefBuilder serializeIdentifier(Identifier identifier);
@@ -125,11 +129,6 @@ abstract class AbstractConstExprSerializer {
   EntityRefBuilder serializeType(TypeName type);
 
   /**
-   * Return [EntityRefBuilder] that corresponds to the given [constructor].
-   */
-  EntityRefBuilder serializeConstructorName(ConstructorName constructor);
-
-  /**
    * Return the [UnlinkedConstBuilder] that corresponds to the state of this
    * serializer.
    */