message: Add to disabled tests the date they were last ran and failed.
  This is to address the comments in cl/186664459.
diff: @@ -698,7 +698,6 @@ INSTANTIATE_TEST_CASE_P(
  #if (XLA_TEST_BACKEND_GPU || XLA_TEST_BACKEND_CPU)
  class Convolve1D1WindowTestHalf : public Convolve1D1WindowTestBase {};
  -// TODO(b/72509305): Enable half data type tests for CPU.
  XLA_TEST_P(Convolve1D1WindowTestHalf, Convolve1D1Window) {
  TestImpl<Eigen::half>();
  }
  @@ -717,8 +716,8 @@ INSTANTIATE_TEST_CASE_P(
  Convolve1DTestParam{130, 1, 1, 1, 3},
  Convolve1DTestParam{64, 1, 1, 1, 1},
  Convolve1DTestParam{128, 1, 1, 1, 1},
  -// TODO(b/72566306): the following five tests fail on CPU
  -// backend due to result miscompare.
  +// TODO(b/72566306): The following five tests failed on CPU with unreasonable
  +// relative errors. Last ran on 2018-02-22.
  #if XLA_TEST_BACKEND_GPU
  Convolve1DTestParam{139, 1, 1, 128, 1},
  Convolve1DTestParam{640, 3, 3, 128, 1},
  