Pushed Variable.from_proto implementation to RefVariable

It was not generic enough to be in the base class.

PiperOrigin-RevId: 222966856

tensorflow/python/ops/resource_variable_ops.py

@@ -1433,7 +1433,7 @@ def _from_proto_fn(v, import_scope=None):
   """Creates Variable or ResourceVariable from VariableDef as needed."""
   if v.is_resource:
     return ResourceVariable.from_proto(v, import_scope=import_scope)
-  return variables.Variable.from_proto(v, import_scope=import_scope)
+  return variables.RefVariable.from_proto(v, import_scope=import_scope)
 
 
 ops.register_proto_function(

tensorflow/python/ops/variables.py

@@ -968,8 +968,7 @@ class Variable(six.with_metaclass(VariableMetaclass,
   @staticmethod
   def from_proto(variable_def, import_scope=None):
     """Returns a `Variable` object created from `variable_def`."""
-    return RefVariable(variable_def=variable_def,
-                       import_scope=import_scope)
+    raise NotImplementedError
 
   class SaveSliceInfo(object):
     """Information on how to save this Variable as a slice.
@@ -2344,6 +2343,12 @@ class RefVariable(VariableV1):
     else:
       return None
 
+  @staticmethod
+  def from_proto(variable_def, import_scope=None):
+    """Returns a `Variable` object created from `variable_def`."""
+    return RefVariable(variable_def=variable_def,
+                       import_scope=import_scope)
+
   def __iadd__(self, other):
     logging.log_first_n(
         logging.WARN,