Store constant variable initializers in elements.

pkg/compiler/lib/src/mirrors/dart2js_mirrors.dart

Index: pkg/compiler/lib/src/mirrors/dart2js_mirrors.dart
diff --git a/pkg/compiler/lib/src/mirrors/dart2js_mirrors.dart b/pkg/compiler/lib/src/mirrors/dart2js_mirrors.dart
index 9ca158b11645bb4282b7392af3111d153c6c37e9..406502a2746f4d6e38b9c847bb525420b41b23ca 100644
--- a/pkg/compiler/lib/src/mirrors/dart2js_mirrors.dart
+++ b/pkg/compiler/lib/src/mirrors/dart2js_mirrors.dart
@@ -463,7 +463,7 @@ class BackDoor {
 
   static ConstantExpression initializerSyntaxOf(Dart2JsFieldMirror variable) {
     Compiler compiler = variable.mirrorSystem.compiler;
-    return compiler.constants.getConstantForVariable(variable._variable);
+    return variable._variable.constant;
   }
 
   static ConstantExpression defaultValueSyntaxOf(
@@ -471,7 +471,7 @@ class BackDoor {
     if (!parameter.hasDefaultValue) return null;
     ParameterElement parameterElement = parameter._element;
     Compiler compiler = parameter.mirrorSystem.compiler;
-    return compiler.constants.getConstantForVariable(parameterElement);
+    return parameterElement.constant;
   }
 
   static Mirror getMirrorFromElement(Dart2JsMirror mirror, Element element) {