Use failedAt in more places (constants, universe)

pkg/compiler/lib/src/constants/constant_constructors.dart

Index: pkg/compiler/lib/src/constants/constant_constructors.dart
diff --git a/pkg/compiler/lib/src/constants/constant_constructors.dart b/pkg/compiler/lib/src/constants/constant_constructors.dart
index 2f8ad07ff4e4b8c4494ff06624b001cb7398299e..2da30e01bfa931fa6d6e2e531085b02c24a27684 100644
--- a/pkg/compiler/lib/src/constants/constant_constructors.dart
+++ b/pkg/compiler/lib/src/constants/constant_constructors.dart
@@ -158,13 +158,13 @@ class ConstantConstructorComputer extends SemanticVisitor
       ConstantExpression defaultValue,
       int index,
       _) {
-    assert(invariant(node, defaultValue != null));
+    assert(defaultValue != null, failedAt(node));
     defaultValues[index] = defaultValue;
   }
 
   visitNamedParameterDeclaration(VariableDefinitions node, Node definition,
       ParameterElement parameter, ConstantExpression defaultValue, _) {
-    assert(invariant(node, defaultValue != null));
+    assert(defaultValue != null, failedAt(node));
     String name = parameter.name;
     defaultValues[name] = defaultValue;
   }
@@ -181,7 +181,7 @@ class ConstantConstructorComputer extends SemanticVisitor
       ConstantExpression defaultValue,
       int index,
       _) {
-    assert(invariant(node, defaultValue != null));
+    assert(defaultValue != null, failedAt(node));
     defaultValues[index] = defaultValue;
     fieldMap[parameter.fieldElement] = new PositionalArgumentReference(index);
   }
@@ -192,7 +192,7 @@ class ConstantConstructorComputer extends SemanticVisitor
       InitializingFormalElement parameter,
       ConstantExpression defaultValue,
       _) {
-    assert(invariant(node, defaultValue != null));
+    assert(defaultValue != null, failedAt(node));
     String name = parameter.name;
     defaultValues[name] = defaultValue;
     fieldMap[parameter.fieldElement] = new NamedArgumentReference(name);