Add Workspace::onDidDestroyPane

This helps with the background-tips conversion

spec/pane-container-spec.coffee

@@ -161,6 +161,21 @@ describe "PaneContainer", ->
 
       expect(events).toEqual [{pane: pane2}, {pane: pane3}]
 
+  describe "::onDidDestroyPane(callback)", ->
+    it "invokes the given callback when panes are destroyed", ->
+      container = new PaneContainer
+      events = []
+      container.onDidDestroyPane (event) -> events.push(event)
+
+      pane1 = container.getActivePane()
+      pane2 = pane1.splitRight()
+      pane3 = pane2.splitDown()
+
+      pane2.destroy()
+      pane3.destroy()
+
+      expect(events).toEqual [{pane: pane2}, {pane: pane3}]
+
   describe "::onWillDestroyPaneItem() and ::onDidDestroyPaneItem", ->
     it "invokes the given callbacks when an item will be destroyed on any pane", ->
       container = new PaneContainer

src/pane-container.coffee

@@ -79,6 +79,9 @@ class PaneContainer extends Model
     fn(pane) for pane in @getPanes()
     @onDidAddPane ({pane}) -> fn(pane)
 
+  onDidDestroyPane: (fn) ->
+    @emitter.on 'did-destroy-pane', fn
+
   onDidChangeActivePane: (fn) ->
     @emitter.on 'did-change-active-pane', fn
 
@@ -193,6 +196,9 @@ class PaneContainer extends Model
   didAddPane: (event) ->
     @emitter.emit 'did-add-pane', event
 
+  didDestroyPane: (event) ->
+    @emitter.emit 'did-destroy-pane', event
+
   # Called by Model superclass when destroyed
   destroyed: ->
     pane.destroy() for pane in @getPanes()

src/pane.coffee

@@ -534,6 +534,7 @@ class Pane extends Model
     @emitter.emit 'did-destroy'
     @emitter.dispose()
     item.destroy?() for item in @items.slice()
+    @container.didDestroyPane(pane: this)
 
   ###
   Section: Splitting

src/workspace.coffee

@@ -233,6 +233,16 @@ class Workspace extends Model
   # Returns a {Disposable} on which `.dispose()` can be called to unsubscribe.
   onDidAddPane: (callback) -> @paneContainer.onDidAddPane(callback)
 
+  # Extended: Invoke the given callback when a pane is destroyed in the
+  # workspace.
+  #
+  # * `callback` {Function} to be called panes are destroyed.
+  #   * `event` {Object} with the following keys:
+  #     * `pane` The destroyed pane.
+  #
+  # Returns a {Disposable} on which `.dispose()` can be called to unsubscribe.
+  onDidDestroyPane: (callback) -> @paneContainer.onDidDestroyPane(callback)
+
   # Extended: Invoke the given callback with all current and future panes in the
   # workspace.
   #