Use failedAt in more places

pkg/compiler/lib/src/diagnostics/invariant.dart

 // Copyright (c) 2012, 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 dart2js.diagnostics.invariant;
 
 import 'spannable.dart';
 
 /**
  * If true, print a warning for each method that was resolved, but not
@@ skipping 17 matching lines @@
 
 /// Throws a [SpannableAssertionFailure].
 ///
 /// Use this method to provide better information for assertion by calling
 /// [failedAt] as the second argument to an `assert` statement:
 ///
 ///     assert(condition, failedAt(position, message));
 ///
 /// [spannable] must be non-null and will be used to provide positional
 /// information in the generated error message.
-bool failedAt(Spannable spannable, [var message]) {
+///
+/// This method can also be used to throw a [SpannableAssertionFailure] outside
+/// an assert:
+///
+///     failedAt(position, message);
+///
+/// or, if the enclosing function requires a result or control flow:
+///
+///     throw failedAt(position, message);
+///
+bool failedAt(Spannable spannable, [String message]) {
   // TODO(johnniwinther): Use [spannable] and [message] to provide better
   // information on assertion errors.
   if (spannable == null) {
-    throw new SpannableAssertionFailure(
-        CURRENT_ELEMENT_SPANNABLE,
-        'Spannable was null for failedInvariant. '
-        'Use CURRENT_ELEMENT_SPANNABLE.');
-  }
-  if (message is Function) {
-    message = message();
+    throw new SpannableAssertionFailure(CURRENT_ELEMENT_SPANNABLE,
+        'Spannable was null for failedAt. Use CURRENT_ELEMENT_SPANNABLE.');
   }
   throw new SpannableAssertionFailure(spannable, message);
 }