use Source.isInSystemLibrary

lib/src/server/server.dart

 // Copyright (c) 2015, 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.
 
 /// Development server that compiles Dart to JS on the fly.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ skipping 131 matching lines @@
     if (_hashing) node.cachingHash = computeHashFromFile(filepath);
   }
 
   void _buildDartLibrary(DartSourceNode node) {
     print('Compiling ${node.uri}');
     var source = node.source;
     // TODO(sigmund): find out from analyzer team if there is a better way
     context.applyChanges(new ChangeSet()..changedSource(source));
     var entryUnit = context.resolveCompilationUnit2(source, source);
     var lib = entryUnit.element.enclosingElement;
-    if (!options.checkSdk && lib.source.uri.scheme == 'dart') return;
+    if (!options.checkSdk && lib.source.isInSystemLibrary) return;
     var current = node.info;
     if (current != null) {
       assert(current.library == lib);
     } else {
       node.info = current = new LibraryInfo(lib);
     }
     _libraries.add(current);
 
     var resolvedParts = node.parts
         .map((p) => context.resolveCompilationUnit2(p.source, source))
@@ skipping 168 matching lines @@
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     var src = resolver.resolveAbsolute(uri, actualUri);
     return src.exists() ? src : null;
   }
 
   Uri restoreAbsolute(Source source) => resolver.restoreAbsolute(source);
 }
 
 final _log = new Logger('dev_compiler.src.server');
 final _earlyErrorResult = new CheckerResults(const [], true);