Create Tasks.Tags endpoint and Cron job

appengine/swarming/handlers_endpoints.py

Index: appengine/swarming/handlers_endpoints.py
diff --git a/appengine/swarming/handlers_endpoints.py b/appengine/swarming/handlers_endpoints.py
index b7ca5d59991ca54d4cc01305ef78d4effab9a86a..5bc4701537d18e1eebcce2cb1f15c7b6f4e3ea4a 100644
--- a/appengine/swarming/handlers_endpoints.py
+++ b/appengine/swarming/handlers_endpoints.py
@@ -423,6 +423,20 @@ class SwarmingTasksService(remote.Service):
         request.state.name.lower(),
         request.tags)
 
+  @gae_ts_mon.instrument_endpoint()
+  @auth.endpoints_method(
+      message_types.VoidMessage, swarming_rpcs.TasksTags,
+      http_method='GET')
+  @auth.require(acl.is_privileged_user)
+  def tags(self, _request):
+    """Returns the cached set of tags currently seen in the fleet."""
+    tags = task_result.TagAggregation.KEY.get()
+    ft = [
+      swarming_rpcs.StringListPair(key=t.tag, value=t.values)
+      for t in tags.tags
+    ]
+    return swarming_rpcs.TasksTags(tasks_tags=ft, ts=tags.ts)
+
 
 BotId = endpoints.ResourceContainer(
     message_types.VoidMessage,