Add 'stopped-changing' event to buffer. Fires 300ms after last change.

This will be used by the status bar and other expensive code that needs to respond to the buffer changing, but that we don't want running on every single keystroke when the user is typing quickly.

spec/app/buffer-spec.coffee

@@ -727,3 +727,23 @@ describe 'Buffer', ->
       expect(buffer.isEmpty()).toBeFalsy()
       buffer.setText('\n')
       expect(buffer.isEmpty()).toBeFalsy()
+
+  describe "stopped-changing event", ->
+    it "fires 'stoppedChangingDelay' ms after the last buffer change", ->
+      delay = buffer.stoppedChangingDelay
+      stoppedChangingHandler = jasmine.createSpy("stoppedChangingHandler")
+      buffer.on 'stopped-changing', stoppedChangingHandler
+
+      buffer.insert([0, 0], 'a')
+      expect(stoppedChangingHandler).not.toHaveBeenCalled()
+
+      advanceClock(delay / 2)
+
+      buffer.insert([0, 0], 'b')
+      expect(stoppedChangingHandler).not.toHaveBeenCalled()
+
+      advanceClock(delay / 2)
+      expect(stoppedChangingHandler).not.toHaveBeenCalled()
+
+      advanceClock(delay / 2)
+      expect(stoppedChangingHandler).toHaveBeenCalled()

src/app/buffer-change-operation.coffee

@@ -41,6 +41,8 @@ class BufferChangeOperation
 
     event = { oldRange, newRange, oldText, newText }
     @buffer.trigger 'change', event
+    @buffer.scheduleStoppedChangingEvent()
+
     anchor.handleBufferChange(event) for anchor in @buffer.getAnchors()
     @buffer.trigger 'update-anchors-after-change'
     newRange

src/app/buffer.coffee

@@ -13,6 +13,8 @@ Git = require 'git'
 module.exports =
 class Buffer
   @idCounter = 1
+  stoppedChangingDelay: 300
+  stoppedChangingTimeout: null
   undoManager: null
   cachedDiskContents: null
   cachedMemoryContents: null
@@ -378,4 +380,11 @@ class Buffer
     if @git?.checkoutHead(path)
       @trigger 'git-status-change'
 
+  scheduleStoppedChangingEvent: ->
+    clearTimeout(@stoppedChangingTimeout) if @stoppedChangingTimeout
+    stoppedChangingCallback = =>
+      @stoppedChangingTimeout = null
+      @trigger 'stopped-changing'
+    @stoppedChangingTimeout = setTimeout(stoppedChangingCallback, @stoppedChangingDelay)
+
 _.extend(Buffer.prototype, EventEmitter)