Use failedAt in more places

pkg/compiler/lib/src/kernel/kernel.dart

 // Copyright (c) 2016, 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.md file.
 
 import 'dart:collection' show Queue;
 
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/verifier.dart' show CheckParentPointers;
 
 import '../common.dart';
@@ skipping 689 matching lines @@
     }
     return false;
   }
 
   ir.Constructor getDartCoreConstructor(
       String className, String constructorName) {
     LibraryElement library =
         compiler.libraryLoader.lookupLibrary(Uris.dart_core);
     ClassElement cls = library.implementation.localLookup(className);
     cls.ensureResolved(compiler.resolution);
-    assert(invariant(CURRENT_ELEMENT_SPANNABLE, cls != null,
-        message: 'dart:core class $className not found.'));
+    assert(
+        cls != null,
+        failedAt(CURRENT_ELEMENT_SPANNABLE,
+            'dart:core class $className not found.'));
     ConstructorElement constructor = cls.lookupConstructor(constructorName);
-    assert(invariant(CURRENT_ELEMENT_SPANNABLE, constructor != null,
-        message: "Constructor '$constructorName' not found "
-            "in class '$className'."));
+    assert(
+        constructor != null,
+        failedAt(CURRENT_ELEMENT_SPANNABLE,
+            "Constructor '$constructorName' not found in class '$className'."));
     compiler.resolution.ensureResolved(constructor);
     return functionToIr(constructor);
   }
 
   ir.Procedure getDartCoreMethod(String name) {
     LibraryElement library =
         compiler.libraryLoader.lookupLibrary(Uris.dart_core);
     Element function = library.implementation.localLookup(name);
-    assert(invariant(CURRENT_ELEMENT_SPANNABLE, function != null,
-        message: "dart:core method '$name' not found."));
+    assert(
+        function != null,
+        failedAt(
+            CURRENT_ELEMENT_SPANNABLE, "dart:core method '$name' not found."));
     compiler.resolution.ensureResolved(function);
     return functionToIr(function);
   }
 
   ir.Procedure getMalformedTypeErrorBuilder() {
     return getDartCoreMethod('_malformedTypeError');
   }
 
   ir.Procedure getUnresolvedConstructorBuilder() {
     return getDartCoreMethod('_unresolvedConstructorError');
@@ skipping 45 matching lines @@
 }
 
 class ConstructorTarget {
   final ConstructorElement element;
   final ResolutionDartType type;
 
   ConstructorTarget(this.element, this.type);
 
   String toString() => "ConstructorTarget($element, $type)";
 }