Add support for .dart files

would-reformat.sh

@@ -58,6 +58,15 @@ elif [[ $file_type == "golang" ]] ; then
         # success
         retval="$exitval"
     fi
+elif [[ $file_type == "dart" ]] ; then
+    success_retval=0
+    would_reformat_retval=1
+    # probably others too :(
+    syntax_error_retval=65
+
+    out=$(dart format -o none --set-exit-if-changed $file)
+    exitval="$?"
+    retval="$exitval"
 else
     echo -n "ignoring"
     exit 0