Cross patch googleapis#470 to ads templates

gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/client.py.j2

@@ -369,6 +369,7 @@ class {{ service.client_name }}(metaclass={{ service.client_name }}Meta):
             method=rpc,
             request=request,
             response=response,
+            metadata=metadata,
         )
         {%- endif %}
         {%- if not method.void %}

gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/pagers.py.j2

@@ -6,7 +6,7 @@
 {# This lives within the loop in order to ensure that this template
    is empty if there are no paged methods.
  -#}
-from typing import Any, Callable, Iterable
+from typing import Any, Callable, Iterable, Sequence, Tuple
 
 {% filter sort_lines -%}
 {% for method in service.methods.values() | selectattr('paged_result_field') -%}
@@ -35,10 +35,10 @@ class {{ method.name }}Pager:
     the most recent response is retained, and thus used for attribute lookup.
     """
     def __init__(self,
-            method: Callable[[{{ method.input.ident }}],
-                {{ method.output.ident }}],
+            method: Callable[..., {{ method.output.ident }}],
             request: {{ method.input.ident }},
-            response: {{ method.output.ident }}):
+            response: {{ method.output.ident }},
+            metadata: Sequence[Tuple[str, str]] = ())):
         """Instantiate the pager.
 
         Args:
@@ -48,10 +48,13 @@ class {{ method.name }}Pager:
                 The initial request object.
             response (:class:`{{ method.output.ident.sphinx }}`):
                 The initial response object.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
         """
         self._method = method
         self._request = {{ method.input.ident }}(request)
         self._response = response
+        self._metadata = metadata
 
     def __getattr__(self, name: str) -> Any:
         return getattr(self._response, name)
@@ -61,7 +64,7 @@ class {{ method.name }}Pager:
         yield self._response
         while self._response.next_page_token:
             self._request.page_token = self._response.next_page_token
-            self._response = self._method(self._request)
+            self._response = self._method(self._request, metadata=self._metadata)
             yield self._response
 
     def __iter__(self) -> {{ method.paged_result_field.ident | replace('Sequence', 'Iterable') }}:

gapic/ads-templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2

@@ -23,6 +23,9 @@ from google.api_core import future
 from google.api_core import operations_v1
 from google.longrunning import operations_pb2
 {% endif -%}
+{% if service.has_pagers -%}
+from google.api_core import gapic_v1
+{% endif -%}
 {% for method in service.methods.values() -%}
 {% for ref_type in method.ref_types
    if not ((ref_type.ident.python_import.package == ('google', 'api_core') and ref_type.ident.python_import.module == 'operation')
@@ -424,9 +427,24 @@ def test_{{ method.name|snake_case }}_pager():
             ),
             RuntimeError,
         )
-        results = [i for i in client.{{ method.name|snake_case }}(
-            request={},
-        )]
+
+        metadata = ()
+        {% if method.field_headers -%}
+        metadata = tuple(metadata) + (
+            gapic_v1.routing_header.to_grpc_metadata((
+                {%- for field_header in method.field_headers %}
+                {%- if not method.client_streaming %}
+                ('{{ field_header }}', ''),
+                {%- endif %}
+                {%- endfor %}
+            )),
+        )
+        {% endif -%}
+        pager = client.{{ method.name|snake_case }}(request={})
+
+        assert pager._metadata == metadata
+
+        results = [i for i in pager]
         assert len(results) == 6
         assert all(isinstance(i, {{ method.paged_result_field.message.ident }})
                    for i in results)