Use failedAt in more places

pkg/compiler/lib/src/deferred_load.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library deferred_load;
 
 import 'common/tasks.dart' show CompilerTask;
 import 'common.dart';
 import 'compiler.dart' show Compiler;
 import 'constants/expressions.dart' show ConstantExpression;
@@ skipping 388 matching lines @@
             if (!expression.isPotential) {
               // Enforce evaluation of [expression].
               backend.constants.getConstantValue(expression);
             }
           }
 
           // Explicitly depend on the backend constants.
           if (backend.constants.hasConstantValue(expression)) {
             ConstantValue value =
                 backend.constants.getConstantValue(expression);
-            assert(invariant(node, value != null,
-                message: "Constant expression without value: "
+            assert(
+                value != null,
+                failedAt(
+                    node,
+                    "Constant expression without value: "
                     "${expression.toStructuredText()}."));
             constants.add(value);
           } else {
             assert(
-                invariant(node, expression.isImplicit || expression.isPotential,
-                    message: "Unexpected unevaluated constant expression: "
-                        "${expression.toStructuredText()}."));
+                expression.isImplicit || expression.isPotential,
+                failedAt(
+                    node,
+                    "Unexpected unevaluated constant expression: "
+                    "${expression.toStructuredText()}."));
           }
         });
       }
     }
 
     // TODO(sigurdm): How is metadata on a patch-class handled?
     for (MetadataAnnotation metadata in element.metadata) {
       ConstantValue constant =
           backend.constants.getConstantValueForMetadata(metadata);
       if (constant != null) {
@@ skipping 662 matching lines @@
 
   bool operator ==(other) {
     if (other is! _DeclaredDeferredImport) return false;
     return declaration == other.declaration;
   }
 
   int get hashCode => declaration.hashCode * 17;
 
   String toString() => '$declaration';
 }