only run the admin server if admin-port is specified

sdk/lib/_internal/pub/lib/src/command/serve.dart

Index: sdk/lib/_internal/pub/lib/src/command/serve.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/serve.dart b/sdk/lib/_internal/pub/lib/src/command/serve.dart
index 1d7db1562df5e226494c9c45b9920f8d0eec1719..0283c2df87c30e106f871d0b345e687018c1763c 100644
--- a/sdk/lib/_internal/pub/lib/src/command/serve.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/serve.dart
@@ -46,9 +46,6 @@ class ServeCommand extends BarbackCommand {
   /// `true` if Dart entrypoints should be compiled to JavaScript.
   bool get useDart2JS => commandOptions['dart2js'];
 
-  /// `true` if the admin server URL should be displayed on startup.
-  bool get logAdminUrl => commandOptions['log-admin-url'];
-
   BarbackMode get defaultMode => BarbackMode.DEBUG;
 
   List<String> get defaultSourceDirectories => ["web", "test"];
@@ -63,11 +60,8 @@ class ServeCommand extends BarbackCommand {
     commandParser.addOption('port', defaultsTo: '8080',
         help: 'The base port to listen on.');
 
-    // TODO(rnystrom): A hidden option to print the URL that the admin server
-    // is bound to on startup. Since this is currently only used for the Web
-    // Socket interface, we don't want to show it to users, but the tests and
-    // Editor need this logged to know what port to bind to.
-    // Remove this (and always log) when #16954 is fixed.
+    // TODO(nweiz): Remove once editor also removes this. This is now a NOOP.
+    // Check on http://dartbug.com/20960
     commandParser.addFlag('log-admin-url', defaultsTo: false, hide: true);
 
     // TODO(nweiz): Make this public when issue 16954 is fixed.
@@ -93,13 +87,13 @@ class ServeCommand extends BarbackCommand {
     var directoryLength = sourceDirectories.map((dir) => dir.length)
         .reduce(math.max);
 
-    var server = await environment.startAdminServer(adminPort);
-    server.results.listen((_) {
-      // The admin server produces no result values.
-      assert(false);
-    }, onError: _fatalError);
+    if (adminPort != null) {
+      var server = await environment.startAdminServer(adminPort);
+      server.results.listen((_) {
+        // The admin server produces no result values.
+        assert(false);
+      }, onError: _fatalError);
 
-    if (logAdminUrl) {
       log.message("Running admin server on "
           "${log.bold('http://$hostname:${server.port}')}");
     }