Use failedAt in more places

pkg/compiler/lib/src/js_backend/namer.dart

 // Copyright (c) 2011, 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 js_backend.namer;
 
 import 'dart:collection' show HashMap;
 
 import 'package:js_runtime/shared/embedded_names.dart' show JsGetName;
 
@@ skipping 478 matching lines @@
   final String nativeSpecProperty = '%';
 
   static final RegExp IDENTIFIER = new RegExp(r'^[A-Za-z_$][A-Za-z0-9_$]*$');
   static final RegExp NON_IDENTIFIER_CHAR = new RegExp(r'[^A-Za-z_0-9$]');
 
   final ClosedWorld _closedWorld;
   final CodegenWorldBuilder _codegenWorldBuilder;
 
   RuntimeTypesEncoder _rtiEncoder;
   RuntimeTypesEncoder get rtiEncoder {
-    assert(invariant(NO_LOCATION_SPANNABLE, _rtiEncoder != null,
-        message: "Namer.rtiEncoder has not been set."));
+    assert(_rtiEncoder != null,
+        failedAt(NO_LOCATION_SPANNABLE, "Namer.rtiEncoder has not been set."));
     return _rtiEncoder;
   }
 
   void set rtiEncoder(RuntimeTypesEncoder value) {
-    assert(invariant(NO_LOCATION_SPANNABLE, _rtiEncoder == null,
-        message: "Namer.rtiEncoder has already been set."));
+    assert(
+        _rtiEncoder == null,
+        failedAt(
+            NO_LOCATION_SPANNABLE, "Namer.rtiEncoder has already been set."));
     _rtiEncoder = value;
   }
 
   /// Used disambiguated names in the global namespace, issued by
   /// [_disambiguateGlobal], and [_disambiguateInternalGlobal].
   ///
   /// Although global names are distributed across a number of global objects,
   /// (see [globalObjectFor]), we currently use a single namespace for all these
   /// names.
   final NamingScope globalScope = new NamingScope();
@@ skipping 1672 matching lines @@
   void addSuggestion(String original, String suggestion) {
     assert(!_suggestedNames.containsKey(original));
     _suggestedNames[original] = suggestion;
   }
 
   bool hasSuggestion(String original) => _suggestedNames.containsKey(original);
   bool isSuggestion(String candidate) {
     return _suggestedNames.containsValue(candidate);
   }
 }