message: Add alloc bytes column to heap summary CSV
  Summary: Useful as is, but also needed in the following diff to write unused capacity somewhere.
diff: @@ -63,6 +63,11 @@ impl FuncInfo {
  fn alloc_count(&self) -> usize {
  self.alloc.values().map(|x| x.count).sum()
  }
  +
  + /// Total number of bytes allocated by this function.
  + fn alloc_bytes(&self) -> usize {
  + self.alloc.values().map(|x| x.bytes).sum()
  + }
  }
  /// We morally have two pieces of information:
  @@ -162,6 +167,7 @@ impl HeapSummaryByFunction {
  "TopCaller",
  "TopCallerCount",
  "Allocs",
  + "AllocBytes",
  ]
  .iter()
  .copied()
  @@ -188,6 +194,7 @@ impl HeapSummaryByFunction {
  csv.write_value(callers.0.as_str());
  csv.write_value(callers.1);
  csv.write_value(info.alloc_count());
  + csv.write_value(info.alloc_bytes());
  for c in &columns {
  csv.write_value(info.alloc.get(c.0).unwrap_or(&AllocCounts::default()).count);
  }
  