Collect a single frame sample in the profiler if we can't validate stack boundaries

runtime/vm/profiler.h

Index: runtime/vm/profiler.h
diff --git a/runtime/vm/profiler.h b/runtime/vm/profiler.h
index 1f65c917a8961dce73d3a9b49dbf7d3f87f879db..096d429ca1da2c3a8076e7b0382e57ceb400b22f 100644
--- a/runtime/vm/profiler.h
+++ b/runtime/vm/profiler.h
@@ -53,6 +53,8 @@ class Profiler : public AllStatic {
                            const InterruptedThreadState& state);
 
  private:
+  // Does not walk the thread's stack.
+  static void SampleThreadSingleFrame(Thread* thread, uintptr_t pc);
   static bool initialized_;
 
   static SampleBuffer* sample_buffer_;