Make sure headful browser closes with beforeuload page (#913)

lib/PuppeteerSharp.Tests/PuppeteerTests/HeadfulTests.cs

@@ -1,10 +1,5 @@
 using System;
-using System.Collections.Generic;
-using System.Diagnostics;
-using System.IO;
 using System.Linq;
-using System.Net;
-using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using PuppeteerSharp.Helpers;
 using Xunit;
@@ -110,6 +105,20 @@ await page.EvaluateFunctionHandleAsync(@"() => {
             }
         }
 
+        [Fact]
+        public async Task ShouldCloseBrowserWithBeforeunloadPage()
+        {
+            var headfulOptions = TestConstants.DefaultBrowserOptions();
+            headfulOptions.Headless = false;
+            using (var browser = await Puppeteer.LaunchAsync(headfulOptions))
+            using (var page = await browser.NewPageAsync())
+            {
+                await page.GoToAsync(TestConstants.ServerUrl + "/beforeunload.html");
+                // We have to interact with a page so that 'beforeunload' handlers fire.
+                await page.ClickAsync("body");
+            }
+        }
+
         private Task<Target> WaitForBackgroundPageTargetAsync(Browser browser)
         {
             var target = browser.Targets().FirstOrDefault(t => t.Type == TargetType.BackgroundPage);