Use failedAt in more places

pkg/compiler/lib/src/parser/element_listener.dart

Index: pkg/compiler/lib/src/parser/element_listener.dart
diff --git a/pkg/compiler/lib/src/parser/element_listener.dart b/pkg/compiler/lib/src/parser/element_listener.dart
index 3ea92c0cb88eabb66e23dab08c526b01d60975b5..d20800f16dac4a2709ec94096dadf51f59117bf8 100644
--- a/pkg/compiler/lib/src/parser/element_listener.dart
+++ b/pkg/compiler/lib/src/parser/element_listener.dart
@@ -788,8 +788,8 @@ class ElementListener extends Listener {
   }
 
   void pushElement(ElementX element) {
-    assert(invariant(element, element.declarationSite != null,
-        message: 'Missing declaration site for $element.'));
+    assert(element.declarationSite != null,
+        failedAt(element, 'Missing declaration site for $element.'));
     popMetadata(element);
     compilationUnitElement.addMember(element, reporter);
   }