add workunit for time to materialize input files in execution sandbox (…

…#12721)

I would like to instrument sandbox setup time (at least for the time it takes to materialize input files). This PR adds a workunit to capture that timing. 

[ci skip-build-wheels]

src/rust/engine/process_execution/src/local.rs

@@ -29,7 +29,7 @@ use tokio::sync::RwLock;
 use tokio::time::{timeout, Duration};
 use tokio_util::codec::{BytesCodec, FramedRead};
 use tryfuture::try_future;
-use workunit_store::{in_workunit, Metric, RunningWorkunit, WorkunitMetadata};
+use workunit_store::{in_workunit, Level, Metric, RunningWorkunit, WorkunitMetadata};
 
 use crate::{
   Context, FallibleProcessResultWithPlatform, MultiPlatformProcess, NamedCaches, Platform, Process,
@@ -467,9 +467,24 @@ pub trait CapturedWorkdir {
     // Start with async materialization of input snapshots, followed by synchronous materialization
     // of other configured inputs. Note that we don't do this in parallel, as that might cause
     // non-determinism when paths overlap.
-    store
-      .materialize_directory(workdir_path.clone(), req.input_files)
-      .await?;
+    let store2 = store.clone();
+    let workdir_path_2 = workdir_path.clone();
+    let input_files = req.input_files;
+    in_workunit!(
+      context.workunit_store.clone(),
+      "setup_sandbox".to_owned(),
+      WorkunitMetadata {
+        level: Level::Trace,
+        ..WorkunitMetadata::default()
+      },
+      |_workunit| async move {
+        store2
+          .materialize_directory(workdir_path_2, input_files)
+          .await
+      },
+    )
+    .await?;
+
     let workdir_path2 = workdir_path.clone();
     let output_file_paths = req.output_files.clone();
     let output_dir_paths = req.output_directories.clone();