message: Use `std::string` instead of `string`
diff: @@ -24,14 +24,14 @@ namespace tflite {
  namespace flex {
  // Get all cpu kernels registered in Tensorflow.
  -std::set<string> GetAllCpuKernels() {
  +std::set<std::string> GetAllCpuKernels() {
  auto is_cpu_kernel = [](const tensorflow::KernelDef& def) {
  return (def.device_type() == "CPU" || def.device_type() == "DEFAULT");
  };
  tensorflow::KernelList kernel_list =
  tensorflow::GetFilteredRegisteredKernels(is_cpu_kernel);
  - std::set<string> result;
  + std::set<std::string> result;
  for (int i = 0; i < kernel_list.kernel_size(); ++i) {
  tensorflow::KernelDef kernel_def = kernel_list.kernel(i);
  @@ -44,7 +44,7 @@ std::set<string> GetAllCpuKernels() {
  // This test must be run on both Linux and Android.
  TEST(AllowlistedFlexOpsTest, EveryOpHasKernel) {
  const std::set<std::string>& allowlist = GetFlexAllowlist();
  - std::set<string> all_kernels = GetAllCpuKernels();
  + std::set<std::string> all_kernels = GetAllCpuKernels();
  for (const std::string& op_name : allowlist) {
  EXPECT_EQ(all_kernels.count(op_name), 1)
  