message: Add comment explaining why breakup-islands pass exists.
diff: @@ -21,6 +21,13 @@ limitations under the License.
  #include "mlir/Pass/PassRegistry.h" // TF:local_config_mlir
  #include "tensorflow/compiler/mlir/tensorflow/ir/tf_executor.h"
  +// This pass is used in preparation for Graph export.
  +// The GraphDef exporter expects each op to be in its own island.
  +// This pass puts the IR in that form.
  +//
  +// We do this as an IR->IR transform to keep the Graph exporter as simple as
  +// possible.
  +
  namespace mlir {
  namespace {
  