[vm] debugger print incomplete async stacktrace

With --trace-debugger-stacktrace being set, debugger will print the stack trace for both async and sync cases. But for async stacktrace, awaiters return call stack are missing from printing.

Change-Id: I2a81ead25bcad5b3b25da4666940f631237352d1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/106441
Reviewed-by: Ben Konyi <[email protected]>
Commit-Queue: Zichang Guo <[email protected]>

Author: zichangg

runtime/vm/debugger.cc

@@ -2470,6 +2470,12 @@ DebuggerStackTrace* Debugger::CollectAwaiterReturnStackTrace() {
     ActivationFrame* activation = new (zone) ActivationFrame(async_activation);
     activation->ExtractTokenPositionFromAsyncClosure();
     stack_trace->AddActivation(activation);
+    if (FLAG_trace_debugger_stacktrace) {
+      OS::PrintErr(
+          "CollectAwaiterReturnStackTrace: visiting awaiter return "
+          "closures:\n\t%s\n",
+          activation->function().ToFullyQualifiedCString());
+    }
     next_async_activation = activation->GetAsyncAwaiter();
     if (next_async_activation.IsNull()) {
       // No more awaiters. Extract the causal stack trace (if it exists).