[Fuchsia] vmservice creates a file in /tmp named with its port.

runtime/bin/vmservice/server.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.
 
 part of vmservice_io;
 
 final bool silentObservatory =
     const bool.fromEnvironment('SILENT_OBSERVATORY');
 
 void serverPrint(String s) {
@@ skipping 326 matching lines @@
         var addresses = await InternetAddress.lookup(_ip);
         // Prefer IPv4 addresses.
         for (var i = 0; i < addresses.length; i++) {
           address = addresses[i];
           if (address.type == InternetAddressType.IP_V4) break;
         }
       }
       _server = await HttpServer.bind(address, _port);
       _server.listen(_requestHandler, cancelOnError: true);
       serverPrint('Observatory listening on $serverAddress');
+      if (Platform.isFuchsia) {
+        // Create a file with the port number.
+        String tmp = Directory.systemTemp.path;
+        String path = "$tmp/dart.services/${_server.port}";
+        serverPrint("Creating $path");
+        new File(path)..createSync(recursive: true);
+      }
       // Server is up and running.
       _notifyServerState(serverAddress.toString());
       onServerAddressChange('$serverAddress');
       return this;
     } catch (e, st) {
       serverPrint('Could not start Observatory HTTP server:\n$e\n$st\n');
       _notifyServerState("");
       onServerAddressChange(null);
       return this;
     }
   }
 
   Future cleanup(bool force) {
     if (_server == null) {
       return new Future.value(null);
     }
+    if (Platform.isFuchsia) {
+      // Remove the file with the port number.
+      String tmp = Directory.systemTemp.path;
+      String path = "$tmp/dart.services/${_server.port}";
+      serverPrint("Deleting $path");
+      new File(path)..deleteSync();
+    }
     return _server.close(force: force);
   }
 
   Future shutdown(bool forced) {
     if (_server == null) {
       // Not started.
       return new Future.value(this);
     }
 
     // Shutdown HTTP server and subscription.
@@ skipping 10 matching lines @@
       _notifyServerState("");
       onServerAddressChange(null);
       return this;
     });
   }
 
 }
 
 void _notifyServerState(String uri)
     native "VMServiceIO_NotifyServerState";