Add a build method to DropoutWrapperBase that passes through to the wrapped cell.

This enables building of cells that have been wrapped with a dropout wrapper.

PiperOrigin-RevId: 265986982

tensorflow/python/ops/rnn_cell_wrapper_impl.py

@@ -194,6 +194,10 @@ class DropoutWrapperBase(object):
   def output_size(self):
     return self.cell.output_size
 
+  def build(self, inputs_shape):
+    self.cell.build(inputs_shape)
+    self.built = True
+
   def zero_state(self, batch_size, dtype):
     with ops.name_scope(type(self).__name__ + "ZeroState", values=[batch_size]):
       return self.cell.zero_state(batch_size, dtype)

tensorflow/tools/api/golden/v1/tensorflow.nn.rnn_cell.-dropout-wrapper.pbtxt

@@ -160,7 +160,7 @@ tf_class {
   }
   member_method {
     name: "build"
-    argspec: "args=[\'self\', \'_\'], varargs=None, keywords=None, defaults=None"
+    argspec: "args=[\'self\', \'inputs_shape\'], varargs=None, keywords=None, defaults=None"
   }
   member_method {
     name: "call"