Implement cudf construction with adapters. (#5189)

src/c_api/c_api.cu

@@ -0,0 +1,20 @@
+// Copyright (c) 2014-2019 by Contributors
+
+#include "xgboost/data.h"
+#include "xgboost/c_api.h"
+#include "c_api_error.h"
+#include "../data/simple_csr_source.h"
+#include "../data/device_adapter.cuh"
+
+namespace xgboost {
+XGB_DLL int XGDMatrixCreateFromArrayInterfaces(char const* c_json_strs,
+                                               bst_int has_missing,
+                                               bst_float missing,
+                                               DMatrixHandle* out) {
+  API_BEGIN();
+  std::string json_str{c_json_strs};
+  data::CudfAdapter adapter(json_str);
+  *out = new std::shared_ptr<DMatrix>(DMatrix::Create(&adapter, missing, 1));
+  API_END();
+}
+}  // namespace xgboost