message: String constants
  Summary: Constants are needed in the following diff
diff: @@ -251,15 +251,19 @@ impl Debug for AggregateHeapProfileInfo {
  }
  impl AggregateHeapProfileInfo {
  + const TOTALS_STR: &'static str = "TOTALS";
  + const ROOT_STR: &'static str = "(root)";
  + const BLANK_STR: &'static str = "";
  +
  pub(crate) fn collect(heap: &Heap, retained: Option<HeapKind>) -> AggregateHeapProfileInfo {
  let mut collector = StackCollector::new(retained);
  unsafe {
  heap.visit_arena(HeapKind::Unfrozen, &mut collector);
  }
  assert_eq!(1, collector.current.len());
  - let totals_id = collector.ids.strings.index("TOTALS");
  - let root_id = collector.ids.strings.index("(root)");
  - let blank_id = collector.ids.strings.index("");
  + let totals_id = collector.ids.strings.index(Self::TOTALS_STR);
  + let root_id = collector.ids.strings.index(Self::ROOT_STR);
  + let blank_id = collector.ids.strings.index(Self::BLANK_STR);
  AggregateHeapProfileInfo {
  strings: collector.ids.strings,
  root: collector.current.pop().unwrap().build(),
  