message: Use Trace for [] in AValue for Array
  Summary: Minor code cleanup.
diff: @@ -621,9 +621,8 @@ impl<'v> AValue<'v> for AValueImpl<Direct, Array<'v>> {
  debug_assert_eq!(content.len(), x.1.len());
  - for elem in content.iter_mut() {
  - tracer.trace(elem);
  - }
  + content.trace(tracer);
  +
  // Note when copying we are dropping extra capacity.
  r.fill(AValueImpl(
  Direct,
  