message: Make caching to be by default True under eager mode.
diff: @@ -1270,6 +1270,10 @@ class SimpleRNNCell(DropoutRNNCellMixin, Layer):
  dropout=0.,
  recurrent_dropout=0.,
  **kwargs):
  + # By default use cached variable under v2 mode, see b/143699808.
  + if ops.executing_eagerly_outside_functions():
  + self._enable_caching_device = kwargs.pop('enable_caching_device', True)
  + else:
  self._enable_caching_device = kwargs.pop('enable_caching_device', False)
  super(SimpleRNNCell, self).__init__(**kwargs)
  self.units = units
  @@ -1701,6 +1705,10 @@ class GRUCell(DropoutRNNCellMixin, Layer):
  implementation=1,
  reset_after=False,
  **kwargs):
  + # By default use cached variable under v2 mode, see b/143699808.
  + if ops.executing_eagerly_outside_functions():
  + self._enable_caching_device = kwargs.pop('enable_caching_device', True)
  + else:
  self._enable_caching_device = kwargs.pop('enable_caching_device', False)
  super(GRUCell, self).__init__(**kwargs)
  self.units = units
  @@ -2255,6 +2263,10 @@ class LSTMCell(DropoutRNNCellMixin, Layer):
  recurrent_dropout=0.,
  implementation=1,
  **kwargs):
  + # By default use cached variable under v2 mode, see b/143699808.
  + if ops.executing_eagerly_outside_functions():
  + self._enable_caching_device = kwargs.pop('enable_caching_device', True)
  + else:
  self._enable_caching_device = kwargs.pop('enable_caching_device', False)
  super(LSTMCell, self).__init__(**kwargs)
  self.units = units
  