Use `Function` as function type syntax.

pkg/compiler/lib/src/common.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 that re-exports libraries used throughout the compiler regardless
 /// of phase or subfunctionality.
 library dart2js.common;
 
 export 'diagnostics/diagnostic_listener.dart'
     show DiagnosticMessage, DiagnosticReporter;
 export 'diagnostics/invariant.dart'
-    show assertDebugMode, InternalErrorFunction, invariant;
+    show assertDebugMode, invariant;
 export 'diagnostics/messages.dart' show MessageKind;
 export 'diagnostics/source_span.dart' show SourceSpan;
 export 'diagnostics/spannable.dart'
     show
         CURRENT_ELEMENT_SPANNABLE,
         NO_LOCATION_SPANNABLE,
         Spannable,
         SpannableAssertionFailure;
 export 'helpers/helpers.dart';