Support serialization of loadLibrary

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

Index: pkg/compiler/lib/src/serialization/constant_serialization.dart
diff --git a/pkg/compiler/lib/src/serialization/constant_serialization.dart b/pkg/compiler/lib/src/serialization/constant_serialization.dart
index b0413471d19c067789d628ef961057682e25264d..ae3040a2d488840b9a3af31d6eb08379ee4aaf5f 100644
--- a/pkg/compiler/lib/src/serialization/constant_serialization.dart
+++ b/pkg/compiler/lib/src/serialization/constant_serialization.dart
@@ -169,8 +169,8 @@ class ConstantSerializer
 
   @override
   void visitDeferred(DeferredConstantExpression exp, ObjectEncoder encoder) {
-    throw new UnsupportedError(
-        "ConstantSerializer.visitDeferred: ${exp.toDartText()}");
+    encoder.setElement(Key.PREFIX, exp.prefix);
+    encoder.setConstant(Key.EXPRESSION, exp.expression);
   }
 }
 
@@ -267,6 +267,9 @@ class ConstantDeserializer {
       case ConstantExpressionKind.NAMED_REFERENCE:
         return new NamedArgumentReference(decoder.getString(Key.NAME));
       case ConstantExpressionKind.DEFERRED:
+        return new DeferredConstantExpression(
+            decoder.getConstant(Key.EXPRESSION),
+            decoder.getElement(Key.PREFIX));
       case ConstantExpressionKind.SYNTHETIC:
     }
     throw new UnsupportedError("Unexpected constant kind: ${kind} in $decoder");