Update git submodules

* Update platform/external/perfetto from branch 'master'
  to b4193168545d5f701d192f4163def93481d53875
  - Merge "Make TracedDictionary/Array implicitly constructible from TracedValue."
  - Make TracedDictionary/Array implicitly constructible from TracedValue.
    
    Allow TracedDictionary & TracedArray to be implicitly constructed from
    TracedValue, similarly to TracedProto<T>.
    
    This will allow to simplify a common case of writing a nested dictionary
    / array from
    
    TRACE_EVENT("cat", "E", "data", [](perfetto::TracedValue ctx) {
      perfetto::TracedDictionary dict = std::move(ctx).WriteDictionary();
      dict.Add(...);
    });
    
    to
    
    TRACE_EVENT("cat", "E", "data", [](perfetto::TracedDictionary dict) {
      dict.Add(...);
    });
    
    R=eseckler@google.com,skyostil@google.com
    CC=​​primiano@google.com
    
    Bug: b/184558843
    Change-Id: If5391ff3f22654a307a04a8faa1b69cc21ecbdaa