I obtained that debug log while testing the arrival of a new message in my inbox:

2015/03/13 11:23:43.310520 DEBUG ping.
2015/03/13 11:23:44.003151 DEBUG got woken up; time is 2015-03-13 11:23:44.002970746 +0000 UTC (𝛥: 2.970746ms)
2015/03/13 11:23:44.008784 DEBUG got wakelock cookie of a506998e-a9a3-44cf-9b65-98bd2dfa7f56
2015/03/13 11:23:44.029309 DEBUG poking polld.
2015/03/13 11:23:44.032596 DEBUG waiting for polld to signal Done.
2015/03/13 11:23:44.326505 DEBUG polld Done.
2015/03/13 11:23:49.332622 DEBUG requested wakeup at 2015-03-13 11:28:49 +0000 UTC
2015/03/13 11:23:49.339149 DEBUG cleared wakelock cookie a506998e-a9a3-44cf-9b65-98bd2dfa7f56.
2015/03/13 11:24:59.711979 DEBUG WatchMethod: ListPersistent(/com/ubuntu/Postal/com_2eubuntu_2edeveloper_2ewebapps_2ewebapp_2dgmail, []interface {}{"com.ubuntu.developer.webapps.webapp-gmail_webapp-gmail"}, []interface {}{(*service.DBusService)(0x9568c2c0)}) success: []string{"[]"}
2015/03/13 11:24:59.715755 DEBUG WatchMethod: Post(/com/ubuntu/Postal/com_2eubuntu_2edeveloper_2ewebapps_2ewebapp_2dgmail, []interface {}{"com.ubuntu.developer.webapps.webapp-gmail_webapp-gmail", "{\"notification\":{\"sound\":\"sounds/ubuntu/notifications/Blip.ogg\",\"card\":{\"summary\":\"David Barth\",\"body\":\"Push notifications\\nThis is a test for push notifications. Let me know if that works... -- David\",\"popup\":true,\"actions\":[\"https://mail.google.com/mail/mu/mp/#cv/priority/^smartlabel_personal/14c12dd0e1f2959d\"],\"persist\":true,\"Timestamp\":1426245616},\"vibrate\":{\"duration\":200},\"tag\":\"gmail\"}}"}, []interface {}{(*service.DBusService)(0x9568c2c0)}) success: []string(nil)
2015/03/13 11:24:59.717963 DEBUG using helper com.ubuntu.developer.webapps.webapp-gmail_webapp-gmail-helper_1.0.25 (exec: /custom/click/com.ubuntu.developer.webapps.webapp-gmail/1.0.25/gmail-helper) for app com.ubuntu.developer.webapps.webapp-gmail_webapp-gmail
2015/03/13 11:24:59.823211 INFO com.ubuntu.developer.webapps.webapp-gmail_webapp-gmail-helper_1.0.25 helper output: {"notification":{"sound":"sounds/ubuntu/notifications/Blip.ogg","card":{"summary":"David Barth","body":"Push notifications\nThis is a test for push notifications. Let me know if that works... -- David","popup":true,"actions":["https://mail.google.com/mail/mu/mp/#cv/priority/^smartlabel_personal/14c12dd0e1f2959d"],"persist":true,"Timestamp":1426245616},"vibrate":{"duration":200},"tag":"gmail"}}
2015/03/13 11:24:59.825856 DEBUG TestURL: [https://mail.google.com/mail/mu/mp/#cv/priority/^smartlabel_personal/14c12dd0e1f2959d]
2015/03/13 11:24:59.862962 DEBUG [09f6df10-fc1f-4e32-9c34-d7e6215176cd] creating popup (or snap decision) for com.ubuntu.developer.webapps.webapp-gmail_webapp-gmail (summary: David Barth)
2015/03/13 11:24:59.867483 DEBUG [09f6df10-fc1f-4e32-9c34-d7e6215176cd] notification has no EmblemCounter: (*launch_helper.EmblemCounter)(nil)
2015/03/13 11:24:59.868041 DEBUG [09f6df10-fc1f-4e32-9c34-d7e6215176cd] notification has no Vibrate.
2015/03/13 11:24:59.873759 DEBUG [09f6df10-fc1f-4e32-9c34-d7e6215176cd] playing sound /usr/share/sounds/ubuntu/notifications/Blip.ogg using paplay
2015/03/13 11:24:59.886893 DEBUG [09f6df10-fc1f-4e32-9c34-d7e6215176cd] creating notification centre entry for com.ubuntu.developer.webapps.webapp-gmail_webapp-gmail (summary: David Barth)
2015/03/13 11:24:59.895538 DEBUG sent dbus signal Post([]interface {}{"com.ubuntu.developer.webapps.webapp-gmail_webapp-gmail"})