Uses Example of Logger with timestamps

You could also do this with a Macro:

Edit > Macros > Start Macro Recording
Code > Reformat with Dart Style
File > Save All
Edit > Macros > Stop Macro Recording
Name the macro, and hit OK

Next, open Preferences, locate Keymap, search for the macro by the name you gave it, right-click, and assign cmd-s to it.

Assorted tips, tricks and knowledge bytes on the dart language and libraries

Dartlang concepts cheatsheet