Revert "dart2js: replace 'invariant' with 'failedAt' to defer interpolation"

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 26 matching lines @@
  *     assert(invariant(position, isValid));
  *
  * [spannable] must be non-null and will be used to provide positional
  * information in the generated error message.
  */
 bool invariant(Spannable spannable, var condition, {var message: null}) {
   // 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 invariant. Use CURRENT_ELEMENT_SPANNABLE.');
+        "Spannable was null for invariant. Use CURRENT_ELEMENT_SPANNABLE.");
   }
   if (condition is Function) {
     condition = condition();
     if (condition is String) {
       message = condition;
       condition = false;
     }
   }
   if (!condition) {
     if (message is Function) {
       message = message();
     }
     throw new SpannableAssertionFailure(spannable, message);
   }
   return true;
 }
 
-/// 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]) {
-  // 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(spannable, message);
-}
-
 typedef void InternalErrorFunction(Spannable location, String message);