Remove AsyncError with Expando.

utils/pub/log.dart

Index: utils/pub/log.dart
diff --git a/utils/pub/log.dart b/utils/pub/log.dart
index ec3fee9798944e586b359b1a0ab0891f78f8d0e0..891ba7d5c18d7d13fdaa7e13273039c6a2ab44c9 100644
--- a/utils/pub/log.dart
+++ b/utils/pub/log.dart
@@ -57,7 +57,16 @@ class Entry {
 }
 
 /// Logs [message] at [Level.ERROR].
-void error(message) => write(Level.ERROR, message);
+void error(message, [error]) {
+  if (error != null) {
+    message = "$message: $error";
+    var trace = getAttachedStackTrace(error);
+    if (trace != null) {
+      message = "$message\nStackTrace: $trace";
+    }
+  }
+  write(Level.ERROR, message);
+}
 
 /// Logs [message] at [Level.WARNING].
 void warning(message) => write(Level.WARNING, message);