Fix compile warnings in Panel.xib

chrome/browser/ui/panels/panel_window_controller_cocoa.mm

Index: chrome/browser/ui/panels/panel_window_controller_cocoa.mm
diff --git a/chrome/browser/ui/panels/panel_window_controller_cocoa.mm b/chrome/browser/ui/panels/panel_window_controller_cocoa.mm
index b002118636ae668f75dbbac0909a5d14a6b581d2..8538f2abacea322e5ef83cd1c0899a2d49aa7087 100644
--- a/chrome/browser/ui/panels/panel_window_controller_cocoa.mm
+++ b/chrome/browser/ui/panels/panel_window_controller_cocoa.mm
@@ -75,20 +75,6 @@ enum {
 - (int)numPanels;
 @end
 
-@interface PanelWindowCocoaImpl : ChromeBrowserWindow {
-  // Panel windows use a higher priority NSWindowLevel to ensure they are always
-  // visible, causing the OS to prefer panel windows when selecting a window
-  // to make the key window. To counter this preference, we override
-  // -[NSWindow:canBecomeKeyWindow] to restrict when the panel can become the
-  // key window to a limited set of scenarios, such as when cycling through
-  // windows, when panels are the only remaining windows, when an event
-  // triggers window activation, etc. The panel may also be prevented from
-  // becoming the key window, regardless of the above scenarios, such as when
-  // a panel is minimized.
-  BOOL canBecomeKey_;  // Defaults to NO.
-}
-@end
-
 @implementation PanelWindowCocoaImpl
 // The panels cannot be reduced to 3-px windows on the edge of the screen
 // active area (above Dock). Default constraining logic makes at least a height