Fix crash caused by not finalizing trace packet

BUG=1102412

Change-Id: I558cbc1b94791354d1b133bf59f5fcb57722387c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2286471Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: ssid <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786353}

services/tracing/public/cpp/stack_sampling/reached_code_data_source_android.cc

@@ -56,6 +56,7 @@ void ReachedCodeDataSource::StopTracing(
     // TODO(ssid): add a new packed field to the trace packet proto.
     streaming_profile_packet->add_callstack_iid(offset);
   }
+  trace_packet->Finalize();
   trace_writer_.reset();
   std::move(stop_complete_callback).Run();
 }