fix: simpleFullscreen window should be on top of other OS X menu bars. (#14881)

If an app has no menu bar (because `app.dock.hide()` has been called),
OS X will still render the menu bar of the previously-focused app.

This commit ensures simpleFullscreen windows will be drawn on top of
that menu bar by setting their level to NSPopUpMenuWindowLevel while
simpleFullscreen mode is active.

Ref: https://github.com/electron/electron/issues/11468

atom/browser/native_window_mac.h

@@ -209,6 +209,7 @@ class NativeWindowMac : public NativeWindow {
   bool was_maximizable_ = false;
   bool was_movable_ = false;
   NSRect original_frame_;
+  NSInteger original_level_;
   NSUInteger simple_fullscreen_mask_;
 
   base::scoped_nsobject<NSColor> background_color_before_vibrancy_;

atom/browser/native_window_mac.mm

@@ -473,6 +473,7 @@ NativeWindowMac::NativeWindowMac(const mate::Dictionary& options,
   AddContentViewLayers();
 
   original_frame_ = [window_ frame];
+  original_level_ = [window_ level];
 }
 
 NativeWindowMac::~NativeWindowMac() {
@@ -892,9 +893,11 @@ void NativeWindowMac::SetSimpleFullScreen(bool simple_fullscreen) {
   if (simple_fullscreen && !is_simple_fullscreen_) {
     is_simple_fullscreen_ = true;
 
-    // Take note of the current window size
-    if (IsNormal())
+    // Take note of the current window size and level
+    if (IsNormal()) {
       original_frame_ = [window_ frame];
+      original_level_ = [window_ level];
+    }
 
     simple_fullscreen_options_ = [NSApp currentSystemPresentationOptions];
     simple_fullscreen_mask_ = [window styleMask];
@@ -911,6 +914,13 @@ void NativeWindowMac::SetSimpleFullScreen(bool simple_fullscreen) {
 
     NSRect fullscreenFrame = [window.screen frame];
 
+    // If our app has dock hidden, set the window level higher so another app's
+    // menu bar doesn't appear on top of our fullscreen app.
+    if ([[NSRunningApplication currentApplication] activationPolicy] !=
+        NSApplicationActivationPolicyRegular) {
+      window.level = NSPopUpMenuWindowLevel;
+    }
+
     if (!fullscreen_window_title()) {
       // Hide the titlebar
       SetStyleMask(false, NSWindowStyleMaskTitled);
@@ -951,6 +961,7 @@ void NativeWindowMac::SetSimpleFullScreen(bool simple_fullscreen) {
         setHidden:window_button_hidden];
 
     [window setFrame:original_frame_ display:YES animate:YES];
+    window.level = original_level_;
 
     [NSApp setPresentationOptions:simple_fullscreen_options_];