message: add dict test case
diff: @@ -1600,13 +1600,25 @@ class BackpropTest(test.TestCase, parameterized.TestCase):
  def outer(x):
  return [x[0]+1, x[1]+1]
  - x = [variables.Variable([1.0, 2.0], name='x'),
  - variables.Variable(1.0, name='x')]
  + x = [variables.Variable([1.0, 2.0], name='a'),
  + variables.Variable(1.0, name='b')]
  with backprop.GradientTape():
  y = outer(x)
  self.assertAllEqual(y[0], [2.0, 3.0])
  self.assertAllEqual(y[1], 2.0)
  + @custom_gradient.recompute_grad
  + def outer_dict(x):
  + for key in x.keys():
  + x[key] = x[key] + 1
  + return x
  + x = {x[0].ref(): x[0], x[1].ref(): x[1]}
  + with backprop.GradientTape():
  + y = outer_dict(x)
  + y = list(y.values())
  + self.assertAllEqual(y[0], [2.0, 3.0])
  + self.assertAllEqual(y[1], 2.0)
  +
  @test_util.assert_no_new_pyobjects_executing_eagerly
  def testRecomputeGradWithNestedFunctionAndWhileLoop(self):
  