Make ping into a message type

This change makes ping into a message type, which
makes the whole protocol a lot more consistent.

Also fixes hacks on the client side to make this all
work.

actioncable/app/assets/javascripts/action_cable/connection.coffee

@@ -73,10 +73,11 @@ class ActionCable.Connection
   events:
     message: (event) ->
       {identifier, message, type} = JSON.parse(event.data)
-
       switch type
         when message_types.welcome
-          @consumer.subscriptions.notify(@consumer.connectionMonitor, "connected")
+          @consumer.connectionMonitor.connected()
+        when message_types.ping
+          @consumer.connectionMonitor.ping()
         when message_types.confirmation
           @consumer.subscriptions.notify(identifier, "connected")
         when message_types.rejection

actioncable/app/assets/javascripts/action_cable/connection_monitor.coffee

@@ -7,10 +7,7 @@ class ActionCable.ConnectionMonitor
 
   @staleThreshold: 6 # Server::Connections::BEAT_INTERVAL * 2 (missed two pings)
 
-  identifier: ActionCable.INTERNAL.identifiers.ping
-
   constructor: (@consumer) ->
-    @consumer.subscriptions.add(this)
     @start()
 
   connected: ->
@@ -22,11 +19,12 @@ class ActionCable.ConnectionMonitor
   disconnected: ->
     @disconnectedAt = now()
 
-  received: ->
+  ping: ->
     @pingedAt = now()
 
   reset: ->
     @reconnectAttempts = 0
+    @consumer.connection.isOpen()
 
   start: ->
     @reset()

actioncable/app/assets/javascripts/action_cable/subscriptions.coffee

@@ -58,7 +58,5 @@ class ActionCable.Subscriptions
 
   sendCommand: (subscription, command) ->
     {identifier} = subscription
-    if identifier is ActionCable.INTERNAL.identifiers.ping
-      @consumer.connection.isOpen()
-    else
     @consumer.send({command, identifier})
+      

actioncable/lib/action_cable.rb

@@ -29,11 +29,9 @@ module ActionCable
   extend ActiveSupport::Autoload
 
   INTERNAL = {
-    identifiers: {
-      ping: '_ping'.freeze
-    },
     message_types: {
       welcome: 'welcome'.freeze,
+      ping: 'ping'.freeze,
       confirmation: 'confirm_subscription'.freeze,
       rejection: 'reject_subscription'.freeze
     }

actioncable/lib/action_cable/connection/base.rb

@@ -114,7 +114,7 @@ module ActionCable
       end
 
       def beat
-        transmit ActiveSupport::JSON.encode(identifier: ActionCable::INTERNAL[:identifiers][:ping], message: Time.now.to_i)
+        transmit ActiveSupport::JSON.encode(type: ActionCable::INTERNAL[:message_types][:ping], message: Time.now.to_i)
       end
 
       def on_open # :nodoc:

actioncable/test/client_test.rb

@@ -75,7 +75,7 @@ class ClientTest < ActionCable::TestCase
 
       @ws.on(:message) do |event|
         hash = JSON.parse(event.data)
-        if hash['identifier'] == '_ping'
+        if hash['type'] == 'ping'
           @pings += 1
         else
           @messages << hash