Use failedAt in more places

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

Index: pkg/compiler/lib/src/serialization/serialization_util.dart
diff --git a/pkg/compiler/lib/src/serialization/serialization_util.dart b/pkg/compiler/lib/src/serialization/serialization_util.dart
index ef8780be8843f9215c2d01d983fd82c03faa2595..f044f73743f82fdce54fe98a32f6acad93786b5b 100644
--- a/pkg/compiler/lib/src/serialization/serialization_util.dart
+++ b/pkg/compiler/lib/src/serialization/serialization_util.dart
@@ -488,8 +488,11 @@ void serializeElementReference(Element context, Key elementKey, Key nameKey,
     ObjectEncoder encoder, Element element) {
   if (element.isGenerativeConstructor &&
       element.enclosingClass.isUnnamedMixinApplication) {
-    assert(invariant(element, element.isConstructor,
-        message: "Unexpected reference of forwarding constructor "
+    assert(
+        element.isConstructor,
+        failedAt(
+            element,
+            "Unexpected reference of forwarding constructor "
             "${element} from $context."));
     encoder.setString(nameKey, element.name);
   } else {
@@ -512,20 +515,29 @@ Element deserializeElementReference(
     }
     ClassElement cls;
     if (context is ClassElement) {
-      assert(invariant(NO_LOCATION_SPANNABLE, context.isNamedMixinApplication,
-          message: "Unexpected reference of forwarding constructor "
+      assert(
+          context.isNamedMixinApplication,
+          failedAt(
+              NO_LOCATION_SPANNABLE,
+              "Unexpected reference of forwarding constructor "
               "'${elementName}' from $context."));
       cls = context;
     } else {
-      assert(invariant(NO_LOCATION_SPANNABLE, context.isConstructor,
-          message: "Unexpected reference of forwarding constructor "
+      assert(
+          context.isConstructor,
+          failedAt(
+              NO_LOCATION_SPANNABLE,
+              "Unexpected reference of forwarding constructor "
               "'${elementName}' from $context."));
       cls = context.enclosingClass;
     }
     ClassElement superclass = cls.superclass;
     element = superclass.lookupConstructor(elementName);
-    assert(invariant(NO_LOCATION_SPANNABLE, element != null,
-        message: "Unresolved reference of forwarding constructor "
+    assert(
+        element != null,
+        failedAt(
+            NO_LOCATION_SPANNABLE,
+            "Unresolved reference of forwarding constructor "
             "'${elementName}' from $context."));
   }
   return element;