Unresolved super-send is not a compile-time error.

dart/frog/leg/compiler.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.
 
 class WorkItem {
   final Element element;
   TreeElements resolutionTree;
   Function run;
   Map<int, BailoutInfo> bailouts = null;
   bool allowSpeculativeOptimization = true;
@@ skipping 356 matching lines @@
   abstract void reportDiagnostic(SourceSpan span, String message, bool fatal);
 
   SourceSpan spanFromTokens(Token begin, Token end) {
     if (begin === null || end === null) {
       // TODO(ahe): We can almost always do better. Often it is only
       // end that is null. Otherwise, we probably know the current
       // URI.
       throw 'cannot find tokens to produce error message';
     }
     final startOffset = begin.charOffset;
-    // TODO(ahe): Compute proper end offset.
+    // TODO(ahe): Compute proper end offset in token. Right now we use
+    // the position of the next token. We want to preserve the
+    // invariant that endOffset > startOffset, but for EOF the
+    // charoffset of the next token may be [startOffset]. This can
+    // also happen for synthetized tokens that are produced during
+    // error handling.
     final endOffset =
-      (end.next !== null) ? end.next.charOffset : startOffset + 1;
+      Math.max((end.next !== null) ? end.next.charOffset : 0, startOffset + 1);
+    assert(endOffset > startOffset);
     Uri uri = currentElement.getCompilationUnit().script.uri;
     return new SourceSpan(uri, startOffset, endOffset);
   }
 
   SourceSpan spanFromNode(Node node) {
     return spanFromTokens(node.getBeginToken(), node.getEndToken());
   }
 
   SourceSpan spanFromElement(Element element) {
     if (element.position() === null) {
@@ skipping 80 matching lines @@
   }
 }
 
 class SourceSpan {
   final Uri uri;
   final int begin;
   final int end;
 
   const SourceSpan(this.uri, this.begin, this.end);
 }