Improvements to causal async stack traces

runtime/vm/debugger.cc

Index: runtime/vm/debugger.cc
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index e234b84c7ac3c5d43de446db7b9e1c50831430eb..0c0edcc769aa9480232142a1447d2ae444b78668 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -1702,6 +1702,10 @@ DebuggerStackTrace* Debugger::CollectAsyncCausalStackTrace() {
       if (async_stack_trace.CodeAtFrame(i) ==
           StubCode::AsynchronousGapMarker_entry()->code()) {
         stack_trace->AddMarker(ActivationFrame::kAsyncSuspensionMarker);
+        // The frame immediately below the asynchronous gap marker is the
+        // identical to the frame above the marker. Skip the frame to enhance
+        // the readability of the trace.
+        i++;
       } else {
         code = Code::RawCast(async_stack_trace.CodeAtFrame(i));
         offset = Smi::RawCast(async_stack_trace.PcOffsetAtFrame(i));