Store constant variable initializers in elements.

pkg/compiler/lib/src/serialization/element_serialization.dart

Index: pkg/compiler/lib/src/serialization/element_serialization.dart
diff --git a/pkg/compiler/lib/src/serialization/element_serialization.dart b/pkg/compiler/lib/src/serialization/element_serialization.dart
index e3d1526e10a1c9046156e7efc0c35dd8a0dd0c3f..6f5dc4d83cd17ded8f670874a3d2e135d65114b3 100644
--- a/pkg/compiler/lib/src/serialization/element_serialization.dart
+++ b/pkg/compiler/lib/src/serialization/element_serialization.dart
@@ -398,8 +398,8 @@ class FieldSerializer implements ElementSerializer {
     encoder.setType(Key.TYPE, element.type);
     encoder.setBool(Key.IS_FINAL, element.isFinal);
     encoder.setBool(Key.IS_CONST, element.isConst);
-    if (element.isConst) {
-      ConstantExpression constant = element.constant;
+    ConstantExpression constant = element.constant;
+    if (constant != null) {
       encoder.setConstant(Key.CONSTANT, constant);
     }
     SerializerUtil.serializeParentRelation(element, encoder);