message: Check all method protos
  Summary: Previously it only checks the protos of methods that have code.
diff: @@ -73,7 +73,6 @@ void process_proto(std::unordered_set<const DexType*>* class_references,
  void process_code(std::unordered_set<const DexType*>* class_references,
  DexMethod* meth,
  IRCode& code) {
  - process_proto(class_references, meth);
  // Types referenced in code.
  for (auto const& mie : InstructionIterable(meth->get_code())) {
  auto opcode = mie.insn;
  @@ -109,10 +108,14 @@ size_t remove_empty_classes(Scope& classes) {
  { process_annotation(&class_references, annotation); });
  // Check the method protos and all the code.
  - walk::code(classes,
  - [](DexMethod*) { return true; },
  - [&](DexMethod* meth, IRCode& code)
  - { process_code(&class_references, meth, code); });
  + walk::methods(classes, [&class_references](DexMethod* meth) {
  + process_proto(&class_references, meth);
  + auto code = meth->get_code();
  + if (!code) {
  + return;
  + }
  + process_code(&class_references, meth, *code);
  + });
  size_t classes_before_size = classes.size();
  