Support compilation of Hello World

pkg/compiler/lib/src/constants/expressions.dart

Index: pkg/compiler/lib/src/constants/expressions.dart
diff --git a/pkg/compiler/lib/src/constants/expressions.dart b/pkg/compiler/lib/src/constants/expressions.dart
index aa284cd20ceb174fe169a5ec994c99f4c2c0eed2..13912f560fe550d6329db74b99746578539bda3e 100644
--- a/pkg/compiler/lib/src/constants/expressions.dart
+++ b/pkg/compiler/lib/src/constants/expressions.dart
@@ -680,8 +680,7 @@ class SymbolConstantExpression extends ConstantExpression {
   @override
   ConstantValue evaluate(
       Environment environment, ConstantSystem constantSystem) {
-    // TODO(johnniwinther): Implement this.
-    throw new UnsupportedError('SymbolConstantExpression.evaluate');
+    return constantSystem.createSymbol(environment.compiler, name);
   }
 
   @override
@@ -1438,7 +1437,9 @@ class DeferredConstantExpression extends ConstantExpression {
   @override
   ConstantValue evaluate(
       Environment environment, ConstantSystem constantSystem) {
-    return expression.evaluate(environment, constantSystem);
+    return new DeferredConstantValue(
+        expression.evaluate(environment, constantSystem),
+        prefix);
   }
 
   @override