message: Fix wide-const test for TF v2
  Summary:
  V2 doesn't have the same namespacing with 'while' in the while_loop,
  and it also was sucessfully eliminating the dynamic slice because we
  were slicing a broadcast constant.
  Manifest tasks:
  T10908
  Test Plan: All tests ok
  Reviewers: #tensorflow, georgep
diff: @@ -72,6 +72,7 @@ class WideConstExpansionTest(xla_test.XLATestCase):
  def body(i, x, y):
  s = array_ops.slice(x, [i, i, i], [1, 1, 2048])
  y = y + math_ops.reduce_mean(s)
  + x = x + constant_op.constant(1, shape=shape, dtype=dtype)
  i = i + 1
  return (i, x, y)
  @@ -90,7 +91,7 @@ class WideConstExpansionTest(xla_test.XLATestCase):
  sess.run(report)
  y = sess.run(r, {y: [10]})
  - self.assertAllClose(y[0], [18])
  + self.assertAllClose(y[0], [19])
  result = sess.run(report)
  self.assertTrue(len(result) == 3)
  @@ -99,8 +100,9 @@ class WideConstExpansionTest(xla_test.XLATestCase):
  cs_list = tu.get_compute_sets_from_report(s)
  ok = [
  - '__seed*', 'Copy_*_to_*', 'while/Slice/dynamic-slice*/dynamicSlice',
  - 'while/Mean/reduce', 'while/Mean/multiply', 'while/add*/add*/AddTo'
  + '__seed*', 'Copy_*_to_*', 'Slice/dynamic-slice*/dynamicSlice',
  + 'Mean/reduce', 'Mean/multiply', 'add*/add*/AddTo',
  + 'add_1_0/fusion/Op/Add'
  ]
  self.assertTrue(tu.check_all_compute_sets_and_list(cs_list, ok))
  