Vendor dependencies for 0.3.0 release

vendor/tracing/benches/span_repeated.rs

@@ -0,0 +1,20 @@
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use tracing::{span, Level};
+
+mod shared;
+
+fn bench(c: &mut Criterion) {
+    shared::for_all_recording(&mut c.benchmark_group("span_repeated"), |b| {
+        let n = black_box(N_SPANS);
+        b.iter(|| (0..n).fold(mk_span(0), |_, i| mk_span(i as u64)))
+    });
+}
+
+#[inline]
+fn mk_span(i: u64) -> tracing::Span {
+    span!(Level::TRACE, "span", i = i)
+}
+
+const N_SPANS: usize = 100;
+criterion_group!(benches, bench);
+criterion_main!(benches);