Add UnlinkedConst.isValid and set it during summarizing.

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 921781d10b7d9934fc923d9f62dd43902d991666..ebaad53af7123bb7ffc852005ca23c5e7ef15b5a 100644
--- a/pkg/analyzer/lib/src/summary/idl.dart
+++ b/pkg/analyzer/lib/src/summary/idl.dart
@@ -516,6 +516,12 @@ abstract class UnlinkedCombinator extends base.SummaryClass {
  */
 abstract class UnlinkedConst extends base.SummaryClass {
   /**
+   * Indicates whether the expression is a valid potentially constant
+   * expression.
+   */
+  bool get isValid;

[Paul Berry, 2016/02/08 15:02:23]

Change this to `isInvalid`.  That way in the normal (valid) case it won't
consume any bytes in the summary file.

[scheglov, 2016/02/08 17:01:42]

Done.

+
+  /**
    * Sequence of operations to execute (starting with an empty stack) to form
    * the constant value.
    */
@@ -1185,8 +1191,9 @@ abstract class UnlinkedParam extends base.SummaryClass {
   int get inferredTypeSlot;
 
   /**
-   * If the parameter has a default value the constant expression in the
-   * default value.
+   * If the parameter has a default value, the constant expression in the
+   * default value.  Note that the presence of this expression does not mean
+   * that it is a valid , check [UnlinkedConst.isValid].
    */
   UnlinkedConst get defaultValue;
 }
@@ -1494,7 +1501,8 @@ abstract class UnlinkedVariable extends base.SummaryClass {
 
   /**
    * If [isConst] is true, and the variable has an initializer, the constant
-   * expression in the initializer.
+   * expression in the initializer.  Note that the presence of this expression
+   * does not mean that it is a valid, check [UnlinkedConst.isValid].
    */
   UnlinkedConst get constExpr;