Adjust the corner radius of fullscreen windows

https://bugs.webkit.org/show_bug.cgi?id=246482
rdar://97042030

Reviewed by Devin Rousso.

* Source/WebKit/UIProcess/ios/fullscreen/WKFullScreenViewController.mm:
(-[WKFullScreenViewController viewIsAppearing:]):

Use `viewIsAppearing` to ensure that the view controller's view has been added
to a window.

* Source/WebKit/UIProcess/ios/fullscreen/WKFullScreenWindowControllerIOS.mm:
(-[WKFullScreenWindowController enterFullScreen:]):

Canonical link: https://commits.webkit.org/255538@main

Source/WebKit/UIProcess/ios/fullscreen/WKFullScreenViewController.mm

@@ -453,6 +453,16 @@ - (void)viewWillAppear:(BOOL)animated
     [super viewWillAppear:animated];
 }
 
+#if HAVE(UIKIT_WEBKIT_INTERNALS)
+- (void)viewIsAppearing:(BOOL)animated
+{
+    self.view.clipsToBounds = YES;
+    self.view._continuousCornerRadius = self.view.window._continuousCornerRadius;
+
+    [super viewIsAppearing:animated];
+}
+#endif
+
 - (void)viewDidLayoutSubviews
 {
     [self _updateWebViewFullscreenInsets];

Source/WebKit/UIProcess/ios/fullscreen/WKFullScreenWindowControllerIOS.mm

@@ -162,7 +162,10 @@ void store(WKWebView* webView)
 
 } // namespace WebKit
 
-static const NSTimeInterval kAnimationDuration = 0.2;
+static constexpr NSTimeInterval kAnimationDuration = 0.2;
+#if HAVE(UIKIT_WEBKIT_INTERNALS)
+static constexpr CGFloat kFullScreenWindowCornerRadius = 12;
+#endif
 
 #pragma mark -
 
@@ -550,6 +553,8 @@ - (void)enterFullScreen:(CGSize)videoDimensions
 #if HAVE(UIKIT_WEBKIT_INTERNALS)
     CGFloat aspectRatio = videoDimensions.height ? (videoDimensions.width / videoDimensions.height) : (960.0 / 540.0);
     [_window setFrame:CGRectMake(0, 0, 540 * aspectRatio, 540)];
+    [_window setClipsToBounds:YES];
+    [_window _setContinuousCornerRadius:kFullScreenWindowCornerRadius];
     [_window setNeedsLayout];
     [_window layoutIfNeeded];
 #endif