Use failedAt in more places

pkg/compiler/lib/src/io/source_information.dart

 // Copyright (c) 2015, 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 dart2js.source_information;
 
 import 'package:kernel/ast.dart' show Location;
 import '../common.dart';
 import '../elements/elements.dart'
     show
@@ skipping 182 matching lines @@
 
   String toString() => '${sourceUri}:[${line},${column}]';
 }
 
 /// A location in a source file.
 abstract class AbstractSourceLocation extends SourceLocation {
   final SourceFile _sourceFile;
   Location _location;
 
   AbstractSourceLocation(this._sourceFile) {
-    assert(invariant(new SourceSpan(sourceUri, 0, 0), isValid,
-        message: "Invalid source location in ${sourceUri}: "
+    assert(
+        isValid,
+        failedAt(
+            new SourceSpan(sourceUri, 0, 0),
+            "Invalid source location in ${sourceUri}: "
             "offset=$offset, length=${_sourceFile.length}."));
   }
 
   /// The absolute URI of the source file of this source location.
   Uri get sourceUri => _sourceFile.uri;
 
   /// The character offset of the this source location into the source file.
   int get offset;
 
   /// The 1-based line number of the [offset].
@@ skipping 101 matching lines @@
   @override
   int get line => null;
 
   @override
   int get offset => null;
 
   String get shortName => '<no-location>';
 
   String toString() => '<no-location>';
 }