Use failedAt in more places

pkg/compiler/lib/src/inferrer/type_system.dart

Index: pkg/compiler/lib/src/inferrer/type_system.dart
diff --git a/pkg/compiler/lib/src/inferrer/type_system.dart b/pkg/compiler/lib/src/inferrer/type_system.dart
index 49af29e6dd476831839c1c6af176023514369c8f..b6d34798cbd70ad26a595981c0280c304a0a7965 100644
--- a/pkg/compiler/lib/src/inferrer/type_system.dart
+++ b/pkg/compiler/lib/src/inferrer/type_system.dart
@@ -68,8 +68,8 @@ class TypeSystem {
   MemberTypeInformation get currentMember => _currentMember;
 
   void withMember(MemberElement element, action) {
-    assert(invariant(element, _currentMember == null,
-        message: "Already constructing graph for $_currentMember."));
+    assert(_currentMember == null,
+        failedAt(element, "Already constructing graph for $_currentMember."));
     _currentMember = getInferredTypeOf(element);
     action();
     _currentMember = null;