RenderWidget popup should be a NSWindow so it can go outside the main window.

ui/base/cocoa/event_hook_application.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_BASE_COCOA_EVENT_HOOK_APPLICATION_H_
+#define UI_BASE_COCOA_EVENT_HOOK_APPLICATION_H_
+
+#ifdef __OBJC__
+
+#import <AppKit/AppKit.h>
+
+#include <vector>
+
+#import "base/memory/scoped_nsobject.h"
+
+// Event hooks must implement this protocol.
+@protocol CrEventHookProtocol
+- (void)hookForEvent:(NSEvent*)theEvent;
+@end
+
+@interface CrEventHookApplication : NSApplication {
+ @private
+  // Array of objects implementing EventHookProtocol.
+  scoped_nsobject<NSMutableArray> eventHooks_;
+}
+
+// Add or remove an event hook to be called for every sendEvent:
+// that the application receives.  These handlers are called before
+// the normal [NSApplication sendEvent:] call is made.
+
+// This is not a good alternative to a nested event loop.  It should
+// be used only when normal event logic and notification breaks down
+// (e.g. when clicking outside a canBecomeKey:NO window to "switch
+// context" out of it).
+- (void)addEventHook:(id<CrEventHookProtocol>)hook;
+- (void)removeEventHook:(id<CrEventHookProtocol>)hook;
+
+@end
+
+#endif
+
+#endif  // UI_BASE_COCOA_EVENT_HOOK_APPLICATION_H_