Replace usage of get_current_toke with StreamToken.START

This allows us to handle /context/ requests on the client_reader worker
without having to pull in all the various stream handlers (e.g.
precence, typing, pushers etc). The only thing the token gets used for
is pagination, and that ignores everything but the room portion of the
token.

synapse/app/client_reader.py

@@ -31,6 +31,7 @@ from synapse.http.site import SynapseSite
 from synapse.metrics import RegistryProxy
 from synapse.metrics.resource import METRICS_PREFIX, MetricsResource
 from synapse.replication.slave.storage._base import BaseSlavedStore
+from synapse.replication.slave.storage.account_data import SlavedAccountDataStore
 from synapse.replication.slave.storage.appservice import SlavedApplicationServiceStore
 from synapse.replication.slave.storage.client_ips import SlavedClientIpStore
 from synapse.replication.slave.storage.directory import DirectoryStore
@@ -58,6 +59,7 @@ logger = logging.getLogger("synapse.app.client_reader")
 
 
 class ClientReaderSlavedStore(
+    SlavedAccountDataStore,
     SlavedEventStore,
     SlavedKeyStore,
     RoomStore,

synapse/handlers/room.py

@@ -24,7 +24,7 @@ from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, JoinRules, RoomCreationPreset
 from synapse.api.errors import AuthError, Codes, StoreError, SynapseError
-from synapse.types import RoomAlias, RoomID, RoomStreamToken, UserID
+from synapse.types import RoomAlias, RoomID, RoomStreamToken, StreamToken, UserID
 from synapse.util import stringutils
 from synapse.visibility import filter_events_for_client
 
@@ -418,8 +418,6 @@ class RoomContextHandler(object):
         before_limit = math.floor(limit / 2.)
         after_limit = limit - before_limit
 
-        now_token = yield self.hs.get_event_sources().get_current_token()
-
         users = yield self.store.get_users_in_room(room_id)
         is_peeking = user.to_string() not in users
 
@@ -462,11 +460,15 @@ class RoomContextHandler(object):
         )
         results["state"] = list(state[last_event_id].values())
 
-        results["start"] = now_token.copy_and_replace(
+        # We use a dummy token here as we only care about the room portion of
+        # the token, which we replace.
+        token = StreamToken.START
+
+        results["start"] = token.copy_and_replace(
             "room_key", results["start"]
         ).to_string()
 
-        results["end"] = now_token.copy_and_replace(
+        results["end"] = token.copy_and_replace(
             "room_key", results["end"]
         ).to_string()