Use isValidConst flag to distinguish between const / final expressions.

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

 // Copyright (c) 2015, 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.
 
 /**
  * This file is an "idl" style description of the summary format.  It
  * contains abstract classes which declare the interface for reading data from
  * summaries.  It is parsed and transformed into code that implements the
  * summary format.
  *
@@ skipping 993 matching lines @@
 
   /**
    * Sequence of unsigned 32-bit integers consumed by the operations
    * `pushArgument`, `pushInt`, `shiftOr`, `concatenate`, `invokeConstructor`,
    * `makeList`, and `makeMap`.
    */
   @Id(1)
   List<int> get ints;
 
   /**
-   * Indicates whether the expression is not a valid potentially constant
+   * Indicates whether the expression is a valid potentially constant
    * expression.
    */
   @Id(5)
-  bool get isInvalid;
+  bool get isValidConst;
 
   /**
    * Sequence of operations to execute (starting with an empty stack) to form
    * the constant value.
    */
   @Id(0)
   List<UnlinkedConstOperation> get operations;
 
   /**
    * Sequence of language constructs consumed by the operations
@@ skipping 1636 matching lines @@
    */
   @Id(11)
   int get visibleLength;
 
   /**
    * If a local variable, the beginning of the visible range; zero otherwise.
    */
   @Id(12)
   int get visibleOffset;
 }