Remove ConstantExpression.value

pkg/compiler/lib/src/resolution/resolution_common.dart

Index: pkg/compiler/lib/src/resolution/resolution_common.dart
diff --git a/pkg/compiler/lib/src/resolution/resolution_common.dart b/pkg/compiler/lib/src/resolution/resolution_common.dart
index d13b5f3c3eca4d3ecc982195aa45e16da94536e5..79741adfcbf52c62f563f8038d502d2eee0ccfa1 100644
--- a/pkg/compiler/lib/src/resolution/resolution_common.dart
+++ b/pkg/compiler/lib/src/resolution/resolution_common.dart
@@ -533,8 +533,9 @@ class ResolverTask extends CompilerTask {
   void _postProcessClassElement(BaseClassElementX element) {
     for (MetadataAnnotation metadata in element.metadata) {
       metadata.ensureResolved(compiler);
-      if (!element.isProxy &&
-          metadata.constant.value == compiler.proxyConstant) {
+      ConstantValue value =
+          compiler.constants.getConstantValue(metadata.constant);
+      if (!element.isProxy && value == compiler.proxyConstant) {
         element.isProxy = true;
       }
     }