Distribution Strategy: Enable eager mode in Keras with MirroredStrategy (Part 1). Will update tests in follow ups.

PiperOrigin-RevId: 223440045

Author: guptapriya

mesh_tensorflow/tpu_variables.py

@@ -172,6 +172,10 @@ def assign_sub(self, delta, use_locking=None, name=None, read_value=True):
   def get(self):
     return self._primary_var
 
+  @property
+  def _in_graph_mode(self):
+    return self._primary_var._in_graph_mode   # pylint: disable=protected-access
+
   def _should_act_as_resource_variable(self):
     """Pass resource_variable_ops.is_resource_variable check."""
     pass