fix: MacOS 26 Tahoe - stop overriding private cornerMask API to fix WindowServer GPU load (#48376)

fix: macOS stop overriding private cornerMask API to fix WindowServer GPU load spike

Electron fetched a custom `_cornerMask` for `ElectronNSWindow` to smooth
vibrancy corners. On macOS 15 (Tahoe) that private hook forces the window
shadow to be rendered from a fully transparent surface, causing the
WindowServer GPU load regression. Remove the `cornerMask` property and
the `_cornerMask` override so we stay on Apple’s default shadow path.

shell/browser/native_window_mac.mm

@@ -1333,7 +1333,6 @@ void NativeWindowMac::UpdateVibrancyRadii(bool fullscreen) {
       maskImage.capInsets = NSEdgeInsetsMake(radius, radius, radius, radius);
       maskImage.resizingMode = NSImageResizingModeStretch;
       [vibrantView setMaskImage:maskImage];
-      [window_ setCornerMask:maskImage];
     }
   }
 }

shell/browser/ui/cocoa/electron_ns_window.h

@@ -40,7 +40,6 @@ class ElectronNativeWindowObserver;
 @property BOOL disableAutoHideCursor;
 @property BOOL disableKeyOrMainWindow;
 @property(nonatomic, retain) NSVisualEffectView* vibrantView;
-@property(nonatomic, retain) NSImage* cornerMask;
 - (id)initWithShell:(electron::NativeWindowMac*)shell
           styleMask:(NSUInteger)styleMask;
 - (void)cleanup;
@@ -48,7 +47,6 @@ class ElectronNativeWindowObserver;
 - (id)accessibilityFocusedUIElement;
 - (NSRect)originalContentRectForFrameRect:(NSRect)frameRect;
 - (BOOL)toggleFullScreenMode:(id)sender;
-- (NSImage*)_cornerMask;
 - (void)disableHeadlessMode;
 @end
 

shell/browser/ui/cocoa/electron_ns_window.mm

@@ -25,7 +25,6 @@ int ScopedDisableResize::disable_resize_ = 0;
 }  // namespace electron
 
 @interface NSWindow (PrivateAPI)
-- (NSImage*)_cornerMask;
 - (int64_t)_resizeDirectionForMouseLocation:(CGPoint)location;
 @end
 
@@ -123,7 +122,6 @@ void SwizzleSwipeWithEvent(NSView* view, SEL swiz_selector) {
 @synthesize disableAutoHideCursor;
 @synthesize disableKeyOrMainWindow;
 @synthesize vibrantView;
-@synthesize cornerMask;
 
 - (id)initWithShell:(electron::NativeWindowMac*)shell
           styleMask:(NSUInteger)styleMask {
@@ -308,16 +306,6 @@ void SwizzleSwipeWithEvent(NSView* view, SEL swiz_selector) {
   return [super validateUserInterfaceItem:item];
 }
 
-// By overriding this built-in method the corners of the vibrant view (if set)
-// will be smooth.
-- (NSImage*)_cornerMask {
-  if (self.vibrantView != nil) {
-    return [self cornerMask];
-  } else {
-    return [super _cornerMask];
-  }
-}
-
 - (void)disableHeadlessMode {
   if (shell_) {
     // We initialize the window in headless mode to allow painting before it is