add chatlist loading benchmark

benches/get_chatlist.rs

@@ -0,0 +1,25 @@
+use criterion::async_executor::AsyncStdExecutor;
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+
+use deltachat::chatlist::Chatlist;
+use deltachat::context::Context;
+
+async fn get_chat_list_benchmark(context: &Context) {
+    Chatlist::try_load(&context, 0, None, None).await.unwrap();
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    // To enable this benchmark, set `DELTACHAT_BENCHMARK_DATABASE` to some large database with many
+    // messages, such as your primary account.
+    if let Ok(path) = std::env::var("DELTACHAT_BENCHMARK_DATABASE") {
+        let context =
+            async_std::task::block_on(async { Context::new(path.into(), 100).await.unwrap() });
+        c.bench_function("chatlist:try_load (Get Chatlist)", |b| {
+            b.to_async(AsyncStdExecutor)
+                .iter(|| get_chat_list_benchmark(black_box(&context)))
+        });
+    }
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);