Add events to manage sheets of macOS BrowserWindow

spec/api-browser-window-spec.js

@@ -1191,6 +1191,54 @@ describe('BrowserWindow module', function () {
     })
   })
 
+  describe('sheet-begin event', function () {
+    if (process.platform !== 'darwin') {
+      return
+    }
+
+    let sheet = null
+
+    afterEach(function () {
+      return closeWindow(sheet, {assertSingleWindow: false}).then(function () { sheet = null })
+    })
+
+    it('emits when window opens a sheet', function (done) {
+      w.show()
+      w.once('sheet-begin', function () {
+        sheet.close()
+        done()
+      })
+      sheet = new BrowserWindow({
+        modal: true,
+        parent: w
+      })
+    })
+  })
+
+  describe('sheet-end event', function () {
+    if (process.platform !== 'darwin') {
+      return
+    }
+
+    let sheet = null
+
+    afterEach(function () {
+      return closeWindow(sheet, {assertSingleWindow: false}).then(function () { sheet = null })
+    })
+
+    it('emits when window has closed a sheet', function (done) {
+      w.show()
+      sheet = new BrowserWindow({
+        modal: true,
+        parent: w
+      })
+      w.once('sheet-end', function () {
+        done()
+      })
+      sheet.close()
+    })
+  })
+
   describe('beginFrameSubscription method', function () {
     // This test is too slow, only test it on CI.
     if (!isCI) return