Use failedAt in more places

pkg/compiler/lib/src/kernel/element_map_mixins.dart

 // Copyright (c) 2017, 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.
 
 import 'package:js_runtime/shared/embedded_names.dart';
 import 'package:kernel/ast.dart' as ir;
 
 import '../common.dart';
 import '../common/names.dart';
 import '../constants/constructors.dart';
@@ skipping 47 matching lines @@
     }
     if (node is ir.PropertySet) {
       return getSetterSelector(node.name);
     }
     if (node is ir.SuperPropertySet) {
       return getSetterSelector(node.name);
     }
     if (node is ir.InvocationExpression) {
       return getInvocationSelector(node);
     }
-    throw new SpannableAssertionFailure(
+    throw failedAt(
         CURRENT_ELEMENT_SPANNABLE,
         "Can only get the selector for a property get or an invocation: "
         "${node}");
   }
 
   Selector getInvocationSelector(ir.InvocationExpression invocation) {
     Name name = getName(invocation.name);
     SelectorKind kind;
     if (Selector.isOperatorName(name.text)) {
       if (name == Names.INDEX_NAME || name == Names.INDEX_SET_NAME) {
@@ skipping 194 matching lines @@
       }
     }
     return null;
   }
 
   ConstantValue getConstantValue(ir.Expression node,
       {bool requireConstant: true, bool implicitNull: false}) {
     ConstantExpression constant;
     if (node == null) {
       if (!implicitNull) {
-        throw new SpannableAssertionFailure(
+        throw failedAt(
             CURRENT_ELEMENT_SPANNABLE, 'No expression for constant.');
       }
       constant = new NullConstantExpression();
     } else {
       constant =
           new Constantifier(this, requireConstant: requireConstant).visit(node);
     }
     if (constant == null) {
       if (requireConstant) {
         throw new UnsupportedError(
@@ skipping 549 matching lines @@
     }
     if (isRedirecting) {
       return new RedirectingGenerativeConstantConstructor(
           defaultValues, superConstructorInvocation);
     } else {
       return new GenerativeConstantConstructor(
           type, defaultValues, fieldMap, superConstructorInvocation);
     }
   }
 }