add an option to send the incremental resolver log to stderr

pkg/analysis_server/lib/src/server/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 'dart:math';
 
@@ skipping 28 matching lines @@
  *     "file:/some/file/name" - log to the file, overwritten on start.
  */
 void _initIncrementalLogger(String spec) {
   logger = NULL_LOGGER;
   if (spec == null) {
     return;
   }
   // create logger
   if (spec == 'console') {
     logger = new StringSinkLogger(stdout);
-  }
-  if (spec.startsWith('file:')) {
+  } else if (spec == 'stderr') {
+    logger = new StringSinkLogger(stderr);
+  } else if (spec.startsWith('file:')) {
     String fileName = spec.substring('file:'.length);
     File file = new File(fileName);
     IOSink sink = file.openWrite();
     logger = new StringSinkLogger(sink);
   }
 }
 
 /// Commandline argument parser. (Copied from analyzer/lib/options.dart)
 /// TODO(pquitslund): replaces with a simple [ArgParser] instance
 /// when the args package supports ignoring unrecognized
@@ skipping 417 matching lines @@
         negatable: false);
     parser.addFlag(ENABLE_INSTRUMENTATION_OPTION,
         help: "enable sending instrumentation information to a server",
         defaultsTo: false,
         negatable: false);
     parser.addFlag(HELP_OPTION,
         help: "print this help message without starting a server",
         defaultsTo: false,
         negatable: false);
     parser.addOption(INCREMENTAL_RESOLUTION_LOG,
-        help: "the description of the incremental resolution log");
+        help: "set a destination for the incremental resolver's log");
     parser.addFlag(INCREMENTAL_RESOLUTION_VALIDATION,
         help: "enable validation of incremental resolution results (slow)",
         defaultsTo: false,
         negatable: false);
     parser.addOption(INSTRUMENTATION_LOG_FILE,
         help:
             "the path of the file to which instrumentation data will be written");
     parser.addFlag(INTERNAL_PRINT_TO_CONSOLE,
         help: "enable sending `print` output to the console",
         defaultsTo: false,
@@ skipping 79 matching lines @@
    */
   static void _rollLogFiles(String path, int numOld) {
     for (int i = numOld - 1; i >= 0; i--) {
       try {
         String oldPath = i == 0 ? path : '$path.$i';
         new File(oldPath).renameSync('$path.${i+1}');
       } catch (e) {}
     }
   }
 }