Ensure custom title bar is always updated when document.title changes

This commit uses a new private API on Workspace that emits an event
every time the window title gets updated (e.g. as a result of an active
pane item changing, the project paths changing, etc.).

This fixes a bug that left the custom title bar with a stale
document.title under some circumstances.

Signed-off-by: Jason Rudolph <jasonrudolph@github.com>

spec/title-bar-spec.coffee

@@ -1,22 +1,27 @@
 TitleBar = require '../src/title-bar'
+temp = require 'temp'
 
 describe "TitleBar", ->
-  it "updates the title based on document.title when the active pane item changes", ->
+  it "updates its title when document.title changes", ->
     titleBar = new TitleBar({
       workspace: atom.workspace,
       themes: atom.themes,
       applicationDelegate: atom.applicationDelegate,
     })
+    expect(titleBar.element.querySelector('.title').textContent).toBe(document.title)
 
-    expect(titleBar.element.querySelector('.title').textContent).toBe document.title
-    initialTitle = document.title
+    paneItem = new FakePaneItem('Title 1')
+    atom.workspace.getActivePane().activateItem(paneItem)
+    expect(document.title).toMatch('Title 1')
+    expect(titleBar.element.querySelector('.title').textContent).toBe(document.title)
 
-    atom.workspace.getActivePane().activateItem({
-      getTitle: -> 'Test Title'
-    })
+    paneItem.setTitle('Title 2')
+    expect(document.title).toMatch('Title 2')
+    expect(titleBar.element.querySelector('.title').textContent).toBe(document.title)
 
-    expect(document.title).not.toBe(initialTitle)
-    expect(titleBar.element.querySelector('.title').textContent).toBe document.title
+    atom.project.setPaths([temp.mkdirSync('project-1')])
+    expect(document.title).toMatch('project-1')
+    expect(titleBar.element.querySelector('.title').textContent).toBe(document.title)
 
   it "can update the sheet offset for the current window based on its height", ->
     titleBar = new TitleBar({
@@ -24,6 +29,19 @@ describe "TitleBar", ->
       themes: atom.themes,
       applicationDelegate: atom.applicationDelegate,
     })
-    expect(->
-      titleBar.updateWindowSheetOffset()
-    ).not.toThrow()
+    expect(-> titleBar.updateWindowSheetOffset()).not.toThrow()
+
+class FakePaneItem
+  constructor: (title) ->
+    @title = title
+
+  getTitle: ->
+    @title
+
+  onDidChangeTitle: (callback) ->
+    @didChangeTitleCallback = callback
+    {dispose: => @didChangeTitleCallback = null}
+
+  setTitle: (title) ->
+    @title = title
+    @didChangeTitleCallback?(title)

src/title-bar.coffee

@@ -10,7 +10,7 @@ class TitleBar
 
     @element.addEventListener 'dblclick', @dblclickHandler
 
-    @workspace.onDidChangeActivePaneItem => @updateTitle()
+    @workspace.onDidChangeWindowTitle => @updateTitle()
     @themes.onDidChangeActiveThemes => @updateWindowSheetOffset()
 
     @updateTitle()

src/workspace.js

@@ -587,6 +587,7 @@ module.exports = class Workspace extends Model {
 
     document.title = titleParts.join(' \u2014 ')
     this.applicationDelegate.setRepresentedFilename(representedPath)
+    this.emitter.emit('did-change-window-title')
   }
 
   // On macOS, fades the application window's proxy icon when the current file
@@ -864,6 +865,10 @@ module.exports = class Workspace extends Model {
     return this.emitter.on('did-add-text-editor', callback)
   }
 
+  onDidChangeWindowTitle (callback) {
+    return this.emitter.on('did-change-window-title', callback)
+  }
+
   /*
   Section: Opening
   */