Default for AggregateHeapProfileInfo

Summary: Empty. Can be used in smoke tests.

Reviewed By: milend

Differential Revision: D38647316

fbshipit-source-id: 2b6c1b6e1c9fa2560c19a9b8f7cffd260cabc8ab

Author: stepancheg

starlark/src/values/layout/heap/profile/aggregated.rs

@@ -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)";