Allow print() to be used for debugging analysis server.

pkg/analysis_server/lib/driver.dart

 // Copyright (c) 2014, 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 driver;
 
+import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/http_server.dart';
 import 'package:analysis_server/src/socket_server.dart';
 import 'package:analysis_server/stdio_server.dart';
 import 'package:analyzer/src/generated/java_io.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/sdk_io.dart';
 import 'package:args/args.dart';
 
@@ skipping 101 matching lines @@
       defaultSdk = DirectoryBasedDartSdk.defaultSdk;
     }
 
     socketServer = new SocketServer(defaultSdk);
     httpServer = new HttpAnalysisServer(socketServer);
     stdioServer = new StdioAnalysisServer(socketServer);
 
     if (serve_http) {
       httpServer.serveHttp(port);
     }
-    stdioServer.serveStdio().then((_) {
-      if (serve_http) {
-        httpServer.close();
-      }
-      exit(0);
-    });
+    _capturePrints(() {
+      stdioServer.serveStdio().then((_) {
+        if (serve_http) {
+          httpServer.close();
+        }
+        exit(0);
+      });
+    }, httpServer.recordPrint);
   }
 
   /**
+   * Execute [callback], capturing any data it prints out and redirecting it to
+   * the function [printHandler].
+   */
+  dynamic _capturePrints(dynamic callback(), void printHandler(String line)) {
+    ZoneSpecification zoneSpecification = new ZoneSpecification(print:
+        (Zone self, ZoneDelegate parent, Zone zone, String line) {
+      printHandler(line);
+      // Note: we don't pass the line on to stdout, because that is reserved
+      // for communication to the client.
+    });
+    return runZoned(callback, zoneSpecification: zoneSpecification);
+  }
+
+  /**
    * Print information about how to use the server.
    */
   void _printUsage(ArgParser parser) {
     print('Usage: $BINARY_NAME [flags]');
     print('');
     print('Supported flags are:');
     print(parser.usage);
   }
 }