Store constant variable initializers in elements.

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

Index: pkg/compiler/lib/src/serialization/modelz.dart
diff --git a/pkg/compiler/lib/src/serialization/modelz.dart b/pkg/compiler/lib/src/serialization/modelz.dart
index 9c346d935b83634ea20b720211b4d32fdf090881..b7f17b3bf7de73ba1457c12e9c696cd98c8f4f76 100644
--- a/pkg/compiler/lib/src/serialization/modelz.dart
+++ b/pkg/compiler/lib/src/serialization/modelz.dart
@@ -1271,6 +1271,7 @@ abstract class FieldElementZ extends DeserializedElementZ
         TypedElementMixin,
         MemberElementMixin
     implements FieldElement {
+  bool _isConst;
   ConstantExpression _constant;
 
   FieldElementZ(ObjectDecoder decoder) : super(decoder);
@@ -1286,14 +1287,22 @@ abstract class FieldElementZ extends DeserializedElementZ
   @override
   bool get isFinal => _decoder.getBool(Key.IS_FINAL);
 
+  void _ensureConstant() {
+    if (_isConst == null) {
+      _isConst = _decoder.getBool(Key.IS_CONST);
+      _constant = _decoder.getConstant(Key.CONSTANT, isOptional: true);
+    }
+  }
+
   @override
-  bool get isConst => _decoder.getBool(Key.IS_CONST);
+  bool get isConst {
+    _ensureConstant();
+    return _isConst;
+  }
 
   @override
   ConstantExpression get constant {
-    if (isConst && _constant == null) {
-      _constant = _decoder.getConstant(Key.CONSTANT);
-    }
+    _ensureConstant();
     return _constant;
   }