[tf.data] Internal refactoring of C++ classes and APIs.

- replacing `OpKernelContext` with newly introduced `DatasetContext` in `DatasetBase` constructor to make it possible to instantiate `DatasetBase` in places where an instance of `OpKernelContext` is not available

- replacing `dataset::MakeIteratorContext(OpKernelContext* ctx)` factory with `IteratorContext(OpKernelContext *ctx)` constructor.

- folding `GraphDatasetBase` into `DataseBase` and removing the default implementation of `AsGraphDefInternal`, making it the responsibility of the derived class to implement it to encourage/hint developers to provide serialization logic

PiperOrigin-RevId: 208560010

1 files changed, 2 insertions, 2 deletions

diff --git a/tensorflow/contrib/kafka/kernels/kafka_dataset_ops.cc b/tensorflow/contrib/kafka/kernels/kafka_dataset_ops.cc
index 92ae79d3c7..d0ea961473 100644
--- a/tensorflow/contrib/kafka/kernels/kafka_dataset_ops.cc
+++ b/tensorflow/contrib/kafka/kernels/kafka_dataset_ops.cc
@@ -52,12 +52,12 @@ class KafkaDatasetOp : public DatasetOpKernel {
   }
 
  private:
-  class Dataset : public GraphDatasetBase {
+  class Dataset : public DatasetBase {
    public:
     Dataset(OpKernelContext* ctx, std::vector<string> topics,
             const string& servers, const string& group, const bool eof,
             const int64 timeout)
-        : GraphDatasetBase(ctx),
+        : DatasetBase(DatasetContext(ctx)),
           topics_(std::move(topics)),
           servers_(servers),
           group_(group),