message: Fix std::cout to TRACE
  Summary: Redex might give more information why some classes/methods are kept by the "whyareyoukeeping" PG option. But it prints out to `std::cout`. Fix them to use `TRACE`.
diff: @@ -301,8 +301,11 @@ void keep_fields(std::unordered_map<std::string, boost::regex*>& regex_map,
  }
  keeper(field);
  if (field->rstate.report_whyareyoukeeping()) {
  - std::cout << "Field " << SHOW(field) << " kept by "
  - << show_keep(keep_rule) << std::endl;
  + TRACE(PGR,
  + 2,
  + "Field %s kept by %s\n",
  + SHOW(field),
  + show_keep(keep_rule).c_str());
  }
  fieldSpecification.count++;
  }
  @@ -397,8 +400,11 @@ void keep_methods(std::unordered_map<std::string, boost::regex*>& regex_map,
  }
  keeper(method);
  if (method->rstate.report_whyareyoukeeping()) {
  - std::cout << "Method " << SHOW(method) << " kept by "
  - << show_keep(keep_rule) << std::endl;
  + TRACE(PGR,
  + 2,
  + "Method %s kept by %s\n",
  + SHOW(method),
  + show_keep(keep_rule).c_str());
  }
  methodSpecification.count++;
  }
  @@ -738,8 +744,8 @@ void process_keep(const ProguardMap& pg_map,
  // may, for instance, forbid renaming of all classes that inherit from a
  // given external class.
  build_extends_or_implements_hierarchy(external_classes, &hierarchy);
  - auto process_single_keep =
  - [&](ClassMatcher& class_match, KeepSpec& keep_rule, DexClass* cls) {
  + auto process_single_keep = [&](
  + ClassMatcher& class_match, KeepSpec& keep_rule, DexClass* cls) {
  // Skip external classes.
  if (cls == nullptr || cls->is_external()) {
  return;
  