Allow Widget to pass accelerator handling to its parent.

ui/views/cocoa/native_widget_mac_accelerator_handler.mm

+// Copyright 2016 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.
+
+#include "ui/views/cocoa/native_widget_mac_accelerator_handler.h"
+
+#include "base/logging.h"
+#include "ui/views/cocoa/native_widget_mac_nswindow.h"
+
+@implementation NativeWidgetMacAcceleratorHandler {
+ @private
+  NSWindow* parent_;
+}
+
+- (instancetype)initWithParentWindow:(NSWindow*)parent {
+  if ((self = [super init])) {
+    DCHECK(parent);
+    parent_ = parent;
+    [[NSNotificationCenter defaultCenter]
+        addObserver:self
+           selector:@selector(parentWindowWillClose:)
+               name:NSWindowWillCloseNotification
+             object:parent_];
+  }
+  return self;
+}
+
+- (void)dealloc {
+  [[NSNotificationCenter defaultCenter] removeObserver:self];
+  [super dealloc];
+}
+
+- (BOOL)validateUserInterfaceItem:(id<NSValidatedUserInterfaceItem>)item
+                           window:(NSWindow*)window {
+  if (!parent_)
+    return NO;
+  id parent = parent_;
+  if ([parent respondsToSelector:@selector(validateUserInterfaceItem:)])
+    return [parent validateUserInterfaceItem:item];
+  return NO;
+}
+
+- (void)commandDispatch:(id)sender window:(NSWindow*)window {
+  id parent = parent_;
+  if ([parent respondsToSelector:@selector(commandDispatch:)])
+    [parent commandDispatch:sender];
+}
+
+- (void)commandDispatchUsingKeyModifiers:(id)sender window:(NSWindow*)window {
+  id parent = parent_;
+  if ([parent respondsToSelector:@selector(commandDispatchUsingKeyModifiers:)])
+    [parent commandDispatchUsingKeyModifiers:sender];
+}
+
+- (void)parentWindowWillClose:(NSNotification*)notification {
+  parent_ = nil;
+}
+
+@end