add example for golang/go#25671

This example demonstrates the bug reported in golang/go#25671

25671/README.md

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+Example for golang/go#25671
+
+Program 25671 demonstrates a bug in shiny/windriver (#25671)
+
+The program creates a main window (blue).
+For any click into the window and a green client window appears.
+Pressing the ESC key asks shiny to close the current window
+by sending a lifecycle event.
+The event loop exits and calls the deferred Release method on the window.
+If this is done on the main window, it works as expected.
+However if it is done on a client window, it does not disappear.
+It is left in an unusable state (try to make it bigger), as the event loop is
+not running anymore.
+
+The fix is mentioned in the issue.

25671/main.go

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+// Program 25671 demonstrates a bug in shiny/windriver (#25671)
+//
+// The program creates a main window (blue).
+// For any click into the window and a green client window appears.
+// Pressing the ESC key asks shiny to close the current window
+// by sending a lifecycle event.
+// The event loop exits and calls the deferred Release method on the window.
+// If this is done on the main window, it works as expected.
+// However if it is done on a client window, it does not disappear.
+// It is left in an unusable state (try to make it bigger), as the event loop is
+// not running anymore.
+package main
+
+import (
+	"image"
+	"image/color"
+	"image/draw"
+	"log"
+
+	"golang.org/x/exp/shiny/driver"
+	"golang.org/x/exp/shiny/screen"
+	"golang.org/x/mobile/event/key"
+	"golang.org/x/mobile/event/lifecycle"
+	"golang.org/x/mobile/event/mouse"
+	"golang.org/x/mobile/event/paint"
+	"golang.org/x/mobile/event/size"
+)
+
+func main() {
+	driver.Main(func(s screen.Screen) {
+		createWindow(s, false)
+	})
+}
+
+func createWindow(s screen.Screen, isClient bool) {
+
+	title := "Main Window"
+	if isClient {
+		title = "Client Window"
+	}
+	opt := screen.NewWindowOptions{Width: 300, Height: 300, Title: title}
+
+	w, err := s.NewWindow(&opt)
+	if err != nil {
+		log.Print(err)
+		return
+	}
+	defer w.Release()
+
+	var b screen.Buffer
+	defer func() {
+		if b != nil {
+			b.Release()
+		}
+	}()
+
+	for {
+		switch e := w.NextEvent().(type) {
+
+		case lifecycle.Event:
+			if e.To == lifecycle.StageDead {
+				log.Printf("received %v: window %p should be closing now", e, w)
+				return
+			}
+
+		case paint.Event:
+			// lock()
+			w.Upload(image.Point{}, b, b.Bounds())
+			w.Publish()
+			// unlock()
+
+		case size.Event:
+			// lock()
+			if b != nil {
+				b.Release()
+			}
+			b, err = s.NewBuffer(e.Size())
+			if err != nil {
+				log.Print(err)
+			}
+
+			// Paint the main window blue, and client windows green.
+			c := color.RGBA{0, 0, 255, 0}
+			if isClient {
+				c = color.RGBA{0, 255, 0, 255}
+			}
+			m := b.RGBA()
+			draw.Draw(m, m.Bounds(), &image.Uniform{c}, image.ZP, draw.Src)
+			// unlock
+
+		case key.Event:
+			// We ask to close the window when the ESC key is pressed.
+			if e.Code == key.CodeEscape && e.Direction == key.DirPress {
+				log.Printf("ESC: send lifecycle.StageDead to window %p", w)
+				e := lifecycle.Event{To: lifecycle.StageDead}
+				w.Send(e)
+			}
+
+		case mouse.Event:
+			if isClient == false {
+				if e.Button > 0 {
+					if e.Direction == mouse.DirPress {
+						log.Print("Create a new window")
+						go createWindow(s, true)
+					}
+				}
+			}
+		}
+	}
+}