Mac: Fix another occurence of the two-windows-have-key-status bug

ui/message_center/cocoa/popup_controller.mm

Index: ui/message_center/cocoa/popup_controller.mm
diff --git a/ui/message_center/cocoa/popup_controller.mm b/ui/message_center/cocoa/popup_controller.mm
index 98cf5dffd0c1fe0eec66cc3cea439aa041bd7031..4991f3bbe22d8efab374beefb470c21ddb45e2f1 100644
--- a/ui/message_center/cocoa/popup_controller.mm
+++ b/ui/message_center/cocoa/popup_controller.mm
@@ -31,7 +31,7 @@
 
 // Window Subclass /////////////////////////////////////////////////////////////
 
-@interface MCPopupWindow : NSPanel {
+@interface MCPopupWindow : NSWindow {
   // The cumulative X and Y scrollingDeltas since the -scrollWheel: event began.
   NSPoint totalScrollDelta_;
 }
@@ -100,8 +100,7 @@
            popupCollection:(MCPopupCollection*)popupCollection {
   base::scoped_nsobject<MCPopupWindow> window(
       [[MCPopupWindow alloc] initWithContentRect:ui::kWindowSizeDeterminedLater
-                                       styleMask:NSBorderlessWindowMask |
-                                                 NSNonactivatingPanelMask
+                                       styleMask:NSBorderlessWindowMask
                                          backing:NSBackingStoreBuffered
                                            defer:NO]);
   if ((self = [super initWithWindow:window])) {