Prompt split editors to save on close

Previously an editor that was split into multiple panes would not
prompt to save correctly when the window was unloading.

This adds a new `windowCloseRequested` option passed through from the
beforeunload handler to the editor so that it can specially handle this
case.

Closes #5257

src/pane-container.coffee

@@ -152,12 +152,12 @@ class PaneContainer extends Model
   saveAll: ->
     pane.saveItems() for pane in @getPanes()
 
-  confirmClose: ->
+  confirmClose: (options) ->
     allSaved = true
 
     for pane in @getPanes()
       for item in pane.getItems()
-        unless pane.promptToSaveItem(item)
+        unless pane.promptToSaveItem(item, options)
           allSaved = false
           break
 

src/pane.coffee

@@ -437,8 +437,8 @@ class Pane extends Model
   destroyInactiveItems: ->
     @destroyItem(item) for item in @getItems() when item isnt @activeItem
 
-  promptToSaveItem: (item) ->
-    return true unless item.shouldPromptToSave?()
+  promptToSaveItem: (item, options={}) ->
+    return true unless item.shouldPromptToSave?(options)
 
     if typeof item.getURI is 'function'
       uri = item.getURI()

src/text-editor.coffee

@@ -641,7 +641,11 @@ class TextEditor extends Model
 
   # Determine whether the user should be prompted to save before closing
   # this editor.
-  shouldPromptToSave: -> @isModified() and not @buffer.hasMultipleEditors()
+  shouldPromptToSave: ({windowCloseRequested}={})->
+    if windowCloseRequested
+      @isModified()
+    else
+      @isModified() and not @buffer.hasMultipleEditors()
 
   ###
   Section: Reading Text

src/window-event-handler.coffee

@@ -52,7 +52,7 @@ class WindowEventHandler
     @subscribe $(window), 'blur', -> document.body.classList.add('is-blurred')
 
     @subscribe $(window), 'beforeunload', =>
-      confirmed = atom.workspace?.confirmClose()
+      confirmed = atom.workspace?.confirmClose(windowCloseRequested: true)
       atom.hide() if confirmed and not @reloadRequested and atom.getCurrentWindow().isWebViewFocused()
       @reloadRequested = false
 

src/workspace.coffee

@@ -599,8 +599,8 @@ class Workspace extends Model
   saveAll: ->
     @paneContainer.saveAll()
 
-  confirmClose: ->
-    @paneContainer.confirmClose()
+  confirmClose: (options) ->
+    @paneContainer.confirmClose(options)
 
   # Save the active pane item.
   #