message: Don't create TpuTracer if the TPU C API isn't initialized.
  Otherwise the profiling APIs will segfault when they attempt to initialize the profile.
diff: @@ -131,6 +131,10 @@ std::unique_ptr<ProfilerInterface> CreateTpuTracer(
  options.device_type() != ProfileOptions::UNSPECIFIED) {
  return nullptr;
  }
  + // Don't attempt to create a TpuTracer if the TPU C API isn't initialized.
  + if (tpu::OpsApiFn()->TpuProfiler_CreateFn == nullptr) {
  + return nullptr;
  + }
  return absl::make_unique<TpuTracer>();
  }
  