title: Using final for Dart parameters
body: <p>I don't see anything on this in the style guide. Moreover, browsing through the Dart SDK code and some pub packages, I do not see any parameters being declared as final. In fact, to get right down to it, I have not seen this done anywhere. (This may just reflect my lack of experience!)</p>
  
  <p>It is manifestly OK to make this declaration, and the Dart editor does use the annotation to flag reassignments as errors.</p>
  
  <p>SO.. is it just too much of a good thing to use final with params, is it not idiomatic Dart, is it in fact a Good Thing, or is there no developed custom with it?</p>