Add logging system to pub and sprinkle some logging in.

utils/pub/git.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Helper functionality for invoking Git.
  */
 library git;
 
 import 'io.dart';
+import 'log.dart' as log;
 import 'utils.dart';
 
 /// Tests whether or not the git command-line app is available for use.
 Future<bool> get isInstalled {
   if (_isGitInstalledCache != null) {
     // TODO(rnystrom): The sleep is to pump the message queue. Can use
     // Future.immediate() when #3356 is fixed.
     return sleep(0).transform((_) => _isGitInstalledCache);
   }
 
@@ skipping 29 matching lines @@
 
   return _tryGitCommand("git").chain((success) {
     if (success) return new Future.immediate("git");
 
     // Git is sometimes installed on Windows as `git.cmd`
     return _tryGitCommand("git.cmd").transform((success) {
       if (success) return "git.cmd";
       return null;
     });
   }).transform((command) {
+    log.fine('Determined git command $command.');
     _gitCommandCache = command;
     return command;
   });
 }
 
 /// Checks whether [command] is the Git command for this computer.
 Future<bool> _tryGitCommand(String command) {
   var completer = new Completer<bool>();
 
   // If "git --version" prints something familiar, git is working.
   var future = runProcess(command, ["--version"]);
 
   future.then((results) {
     var regex = new RegExp("^git version");
     completer.complete(results.stdout.length == 1 &&
                        regex.hasMatch(results.stdout[0]));
   });
 
   future.handleException((err) {
     // If the process failed, they probably don't have it.
     completer.complete(false);
     return true;
   });
 
   return completer.future;
 }