function keep(result) {
	  return ENGINE.keep(result);
	}
Keeps a `tf.Tensor` generated inside a `tf.tidy` from being disposed
automatically.

```js
let b;
const y = tf.tidy(() => {
  const one = tf.scalar(1);
  const a = tf.scalar(2);

  // b will not be cleaned up by the tidy. a and one will be cleaned up
  // when the tidy ends.
  b = tf.keep(a.square());

  console.log('numTensors (in tidy): ' + tf.memory().numTensors);

  // The value returned inside the tidy function will return
  // through the tidy, in this case to the variable y.
  return b.add(one);
});

console.log('numTensors (outside tidy): ' + tf.memory().numTensors);
console.log('y:');
y.print();
console.log('b:');
b.print();
```

@param result The tensor to keep from being disposed.

@doc {heading: 'Performance', subheading: 'Memory'}