Add SILENT_OBSERVATORY environment variable to Observatory web server

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) {
+  if (silentObservatory) {
+    // We've been requested to be silent.
+    return;
+  }
+  print(s);
+}
+
 class WebSocketClient extends Client {
   static const int PARSE_ERROR_CODE = 4000;
   static const int BINARY_MESSAGE_ERROR_CODE = 4001;
   static const int NOT_MAP_ERROR_CODE = 4002;
   static const int ID_ERROR_CODE = 4003;
   final WebSocket socket;
 
   WebSocketClient(this.socket, VMService service) : super(service) {
     socket.listen((message) => onWebSocketMessage(message));
     socket.done.then((_) => close());
@@ skipping 36 matching lines @@
     try {
       if (result is String || result is Uint8List) {
         socket.add(result);  // String or binary message.
       } else {
         // String message as external Uint8List.
         assert(result is List);
         Uint8List cstring = result[0];
         socket.addUtf8Text(cstring);
       }
     } catch (e, st) {
-      print("Ignoring error posting over WebSocket.");
-      print(e);
-      print(st);
+      serverPrint("Ignoring error posting over WebSocket.");
+      serverPrint(e);
+      serverPrint(st);
     }
   }
 
   dynamic toJson() {
     Map map = super.toJson();
     map['type'] = 'WebSocketClient';
     map['socket'] = '$socket';
     return map;
   }
 }
@@ skipping 209 matching lines @@
       request.response.add(asset.data);
       request.response.close();
       return;
     }
     // HTTP based service request.
     try {
       var client = new HttpRequestClient(request, _service);
       var message = new Message.fromUri(client, request.uri);
       client.onMessage(null, message);
     } catch (e) {
-      print('Unexpected error processing HTTP request uri: '
-            '${request.uri}\n$e\n');
+      serverPrint('Unexpected error processing HTTP request uri: '
+                  '${request.uri}\n$e\n');
       rethrow;
     }
   }
 
   Future startup() async {
     if (_server != null) {
       // Already running.
       return this;
     }
 
     // Startup HTTP server.
     try {
       var address;
       if (Platform.isFuchsia) {
         address = InternetAddress.ANY_IP_V6;
       } else {
         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);
-      print('Observatory listening on $serverAddress');
+      serverPrint('Observatory listening on $serverAddress');
       // Server is up and running.
       _notifyServerState(serverAddress.toString());
       onServerAddressChange('$serverAddress');
       return this;
     } catch (e, st) {
-      print('Could not start Observatory HTTP server:\n$e\n$st\n');
+      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);
     }
     return _server.close(force: force);
   }
 
   Future shutdown(bool forced) {
     if (_server == null) {
       // Not started.
       return new Future.value(this);
     }
 
     // Shutdown HTTP server and subscription.
     Uri oldServerAddress = serverAddress;
     return cleanup(forced).then((_) {
-      print('Observatory no longer listening on $oldServerAddress');
+      serverPrint('Observatory no longer listening on $oldServerAddress');
       _server = null;
       _notifyServerState("");
       onServerAddressChange(null);
       return this;
     }).catchError((e, st) {
       _server = null;
-      print('Could not shutdown Observatory HTTP server:\n$e\n$st\n');
+      serverPrint('Could not shutdown Observatory HTTP server:\n$e\n$st\n');
       _notifyServerState("");
       onServerAddressChange(null);
       return this;
     });
   }
 
 }
 
 void _notifyServerState(String uri)
     native "VMServiceIO_NotifyServerState";