Add support for .dart files

_reformat-common.sh

@@ -29,6 +29,8 @@ function sniff_file_type() {
         file_type="sh"
     elif [[ $ff = *.go ]] ; then
         file_type="golang"
+    elif [[ $ff = *.dart ]] ; then
+        file_type="dart"
     fi
 
     echo $file_type