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 c911061fdc3c5c367e992fffe9782cf97daea261..ee52e0f45e0024639441798fabbda20d29ea18a1 100644
--- a/pkg/analyzer/lib/src/summary/idl.dart
+++ b/pkg/analyzer/lib/src/summary/idl.dart
@@ -521,6 +521,12 @@ abstract class UnlinkedCombinator extends base.SummaryClass {
  */
 abstract class UnlinkedConst extends base.SummaryClass {
   /**
+   * Indicates whether the expression is not a valid potentially constant
+   * expression.
+   */
+  bool get isInvalid;
+
+  /**
    * Sequence of operations to execute (starting with an empty stack) to form
    * the constant value.
    */
@@ -1277,8 +1283,9 @@ 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].

[Paul Berry, 2016/02/08 17:07:41]

Missing a word here.  I think you mean: "...that it is a valid constant; check
[UnlinkedConst.isInvalid]."

    */
   UnlinkedConst get defaultValue;
 }
@@ -1612,7 +1619,8 @@ 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].

[Paul Berry, 2016/02/08 17:07:41]

Similar comment here.

    */
   UnlinkedConst get constExpr;