message: Default for AggregateHeapProfileInfo
  Summary: Empty. Can be used in smoke tests.
diff: @@ -196,7 +196,7 @@ impl<'v> ArenaVisitor<'v> for StackCollector {
  }
  /// Aggregated stack frame data.
  -#[derive(Clone)]
  +#[derive(Clone, Default)]
  pub(crate) struct StackFrame {
  /// Aggregated callees.
  pub(crate) callees: SmallMap<StringId, StackFrame>,
  @@ -310,6 +310,22 @@ impl Debug for AggregateHeapProfileInfo {
  }
  }
  +impl Default for AggregateHeapProfileInfo {
  + fn default() -> AggregateHeapProfileInfo {
  + let mut strings = StringIndex::default();
  + let totals_id = strings.index(AggregateHeapProfileInfo::TOTALS_STR);
  + let root_id = strings.index(AggregateHeapProfileInfo::ROOT_STR);
  + let blank_id = strings.index(AggregateHeapProfileInfo::BLANK_STR);
  + AggregateHeapProfileInfo {
  + root: StackFrame::default(),
  + strings,
  + totals_id,
  + root_id,
  + blank_id,
  + }
  + }
  +}
  +
  impl AggregateHeapProfileInfo {
  const TOTALS_STR: &'static str = "TOTALS";
  const ROOT_STR: &'static str = "(root)";
  