-Fix display of megamorphic miss function.

runtime/observatory/lib/src/elements/script_inset.dart

 // Copyright (c) 2013, 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 script_inset_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'observatory_element.dart';
 import 'service_ref.dart';
@@ skipping 526 matching lines @@
                    ? (script.tokenToCol(currentPos))
                    : null);
     if (_currentCol != null) {
       _currentCol--;  // make this 0-based.
     }
 
     _endLine = (endPos != null
                 ? script.tokenToLine(endPos)
                 : script.lines.length + script.lineOffset);
 
+    if (_startLine == null || _endLine == null) {
+      return;
+    }
+
     annotations.clear();
 
     addCurrentExecutionAnnotation();
     addBreakpointAnnotations();
 
     if (!inDebuggerContext && script.library != null) {
       if (hasLoadedLibraryDeclarations) {
         addLibraryAnnotations();
         addDependencyAnnotations();
         addPartAnnotations();
@@ skipping 461 matching lines @@
 @CustomTag('source-inset')
 class SourceInsetElement extends PolymerElement {
   SourceInsetElement.created() : super.created();
 
   @published SourceLocation location;
   @published String height = null;
   @published int currentPos;
   @published bool inDebuggerContext = false;
   @published ObservableList variables;
 }