Remove SetConnectedSubchannelFromLocked().

src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc

@@ -332,9 +332,13 @@ void PickFirst::UpdateLocked(const grpc_channel_args& args) {
                   this, selected_->subchannel(), i,
                   subchannel_list->num_subchannels());
         }
-        if (selected_->connected_subchannel() != nullptr) {
-          sd->SetConnectedSubchannelFromLocked(selected_);
-        }
+        // Make sure it's in state READY.  It might not be if we grabbed
+        // the combiner while a connectivity state notification
+        // informing us otherwise is pending.
+        // Note that CheckConnectivityStateLocked() also takes a ref to
+        // the connected subchannel.
+        grpc_error* error = GRPC_ERROR_NONE;
+        if (sd->CheckConnectivityStateLocked(&error) == GRPC_CHANNEL_READY) {
           selected_ = sd;
           subchannel_list_ = std::move(subchannel_list);
           DestroyUnselectedSubchannelsLocked();
@@ -346,6 +350,7 @@ void PickFirst::UpdateLocked(const grpc_channel_args& args) {
           return;
         }
       }
+    }
     // Not keeping the previous selected subchannel, so set the latest
     // pending subchannel list to the new subchannel list.  We will wait
     // for it to report READY before swapping it into the current

src/core/ext/filters/client_channel/lb_policy/subchannel_list.h

@@ -89,20 +89,6 @@ class SubchannelData {
     return connected_subchannel_.get();
   }
 
-// FIXME: remove
-  // Used to set the connected subchannel in cases where we are retaining a
-  // subchannel from a previous subchannel list.  This is slightly more
-  // efficient than getting the connected subchannel from the subchannel,
-  // because that approach requires the use of a mutex, whereas this one
-  // only mutates a refcount.
-  // TODO(roth): This method is a bit of a hack and is used only in
-  // pick_first.  When we have time, find a way to remove this, possibly
-  // by making pick_first work more like round_robin.
-  void SetConnectedSubchannelFromLocked(SubchannelData* other) {
-    GPR_ASSERT(subchannel_ == other->subchannel_);
-    connected_subchannel_ = other->connected_subchannel_;  // Adds ref.
-  }
-
   // Synchronously checks the subchannel's connectivity state.
   // Must not be called while there is a connectivity notification
   // pending (i.e., between calling StartConnectivityWatchLocked() or