message: Add definition for static `FunctionLibraryDefinition` constants.
diff: @@ -40,6 +40,17 @@ limitations under the License.
  namespace tensorflow {
  +/* static */ constexpr const char* const FunctionLibraryDefinition::kArgOp;
  +/* static */ constexpr const char* const
  + FunctionLibraryDefinition::kDeviceArgOp;
  +/* static */ constexpr const char* const FunctionLibraryDefinition::kRetOp;
  +/* static */ constexpr const char* const
  + FunctionLibraryDefinition::kDeviceRetOp;
  +/* static */ constexpr const char* const
  + FunctionLibraryDefinition::kIntsOnDeviceAttr;
  +/* static */ constexpr const char* const FunctionLibraryDefinition::kGradientOp;
  +/* static */ constexpr const char* const FunctionLibraryDefinition::kFuncAttr;
  +
  // Extracts the actual type from "attr_values" based on its definition
  // "arg_def".
  //
  