Add logging system to pub and sprinkle some logging in.

utils/pub/entrypoint.dart

Index: utils/pub/entrypoint.dart
diff --git a/utils/pub/entrypoint.dart b/utils/pub/entrypoint.dart
index d3af1fa53f92055e85d854aeed926ee7909ad1ed..b9585d5649867d7af94b71759d59fa1b039c85dc 100644
--- a/utils/pub/entrypoint.dart
+++ b/utils/pub/entrypoint.dart
@@ -6,6 +6,7 @@ library entrypoint;
 
 import 'io.dart';
 import 'lock_file.dart';
+import 'log.dart' as log;
 import 'package.dart';
 import 'root_source.dart';
 import 'system_cache.dart';
@@ -87,6 +88,7 @@ class Entrypoint {
       if (!exists) return new Future.immediate(null);
       // TODO(nweiz): figure out when to actually delete the directory, and when
       // we can just re-use the existing symlink.
+      log.fine("Deleting package directory for ${id.name} before install.");
       return deleteDir(packageDir);
     }).chain((_) {
       if (id.source.shouldCache) {
@@ -167,6 +169,8 @@ class Entrypoint {
   Future<LockFile> _loadLockFile() {
     var completer = new Completer<LockFile>();
     var lockFilePath = join(root.dir, 'pubspec.lock');
+
+    log.fine("Loading lockfile.");
     var future = readTextFile(lockFilePath);
 
     future.handleException((_) {
@@ -174,8 +178,9 @@ class Entrypoint {
       // probably wrong and we should notify the user.
       fileExists(lockFilePath).transform((exists) {
         if (!exists) return;
-        printError("Error reading pubspec.lock: ${future.exception}");
+        log.error("Error reading pubspec.lock: ${future.exception}");
       }).then((_) {
+        log.fine("No lock file at $lockFilePath, creating empty one.");
         completer.complete(new LockFile.empty());
       });
 
@@ -196,7 +201,9 @@ class Entrypoint {
       if (id.source is! RootSource) lockFile.packages[id.name] = id;
     }
 
-    return writeTextFile(join(root.dir, 'pubspec.lock'), lockFile.serialize());
+    var lockFilePath = join(root.dir, 'pubspec.lock');
+    log.fine("Saving lockfile.");
+    return writeTextFile(lockFilePath, lockFile.serialize());
   }
 
   /**