macos crash on closing a fullscreen window

[lavv17]

On macos, there is a crash when trying to close a fullscreen window using CloseBrowser. It happens because there is no "setDelegate:nil" call on the window before destruction of CefWindowDelegate object.

Thread 0 Crashed:: CrBrowserMain Dispatch queue: com.apple.main-thread
0 libobjc.A.dylib 0x00007fffc27b6b5d objc_msgSend + 29
1 com.apple.AppKit 0x00007fffabd30b4a -[NSWindow _confirmSize:force:] + 216
2 com.apple.AppKit 0x00007fffabf778fb -[NSWindow _frameOnExitFromFullScreen] + 134
3 com.apple.AppKit 0x00007fffabf79ec8 -[NSWindow _didExitFullScreen:] + 170
4 com.apple.AppKit 0x00007fffac5fd2fb __123-[_NSWindowFullScreenTransition _performExitFullScreenModeForWindow:windowController:options:customWindows:doKitAnimation:]_block_invoke_2 + 390
5 com.apple.AppKit 0x00007fffac5fd081 __123-[_NSWindowFullScreenTransition _performExitFullScreenModeForWindow:windowController:options:customWindows:doKitAnimation:]_block_invoke + 1191
6 com.apple.AppKit 0x00007fffac147634 __NSFullScreenDockConnectionSendExitForTransition_block_invoke + 88

[magreenblatt]

Please add a bug. A PR to fix the issue is also welcome.