Update git submodules

* Update platform/external/perfetto from branch 'master'
  to 981be5ab5ba9674eded95ed5493811a061d7ed2a
  - Merge "Support TraceFormatTraits for TracedProto"
  - Support TraceFormatTraits for TracedProto
    
    In addition to T::WriteIntoTrace(TracedProto<Message>) allow users to
    define perfetto::TraceFormatTraits<T>::WriteIntoTrace to define how
    a given class |T| should be serialised into a trace.
    
    R=skyostil@google.com,eseckler@google.com
    
    Bug: b/184558843
    Change-Id: I3d5ac10f31073208bb1e0239a10b186daf554994