Use failedAt in more places (js_emitter)

pkg/compiler/lib/src/js_emitter/type_test_registry.dart

Index: pkg/compiler/lib/src/js_emitter/type_test_registry.dart
diff --git a/pkg/compiler/lib/src/js_emitter/type_test_registry.dart b/pkg/compiler/lib/src/js_emitter/type_test_registry.dart
index b6dc0d0ed70a5c3239274c20041ede5ce26c8ade..2377a5541b8abbe51c2111e174b6355fcf42ce3c 100644
--- a/pkg/compiler/lib/src/js_emitter/type_test_registry.dart
+++ b/pkg/compiler/lib/src/js_emitter/type_test_registry.dart
@@ -69,14 +69,18 @@ class TypeTestRegistry {
       this._codegenWorldBuilder, this._closedWorld, this._elementEnvironment);
 
   RuntimeTypesChecks get rtiChecks {
-    assert(invariant(NO_LOCATION_SPANNABLE, _rtiChecks != null,
-        message: "RuntimeTypesChecks has not been computed yet."));
+    assert(
+        _rtiChecks != null,
+        failedAt(NO_LOCATION_SPANNABLE,
+            "RuntimeTypesChecks has not been computed yet."));
     return _rtiChecks;
   }
 
   Iterable<ClassEntity> get rtiNeededClasses {
-    assert(invariant(NO_LOCATION_SPANNABLE, _rtiNeededClasses != null,
-        message: "rtiNeededClasses has not been computed yet."));
+    assert(
+        _rtiNeededClasses != null,
+        failedAt(NO_LOCATION_SPANNABLE,
+            "rtiNeededClasses has not been computed yet."));
     return _rtiNeededClasses;
   }