[Mac] Disable menu certain menu items when a modal dialog or sheet is present.

chrome/browser/cocoa/history_menu_cocoa_controller.mm

Index: chrome/browser/cocoa/history_menu_cocoa_controller.mm
diff --git a/chrome/browser/cocoa/history_menu_cocoa_controller.mm b/chrome/browser/cocoa/history_menu_cocoa_controller.mm
index 8e3f6728ac2c9b14ba7bffc0f22dba26bde6165a..1b6241e9c7d6c9e962c4daae0063be837059507d 100644
--- a/chrome/browser/cocoa/history_menu_cocoa_controller.mm
+++ b/chrome/browser/cocoa/history_menu_cocoa_controller.mm
@@ -2,11 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#import "chrome/browser/cocoa/history_menu_cocoa_controller.h"
+
 #include "base/scoped_vector.h"
 #include "chrome/app/chrome_dll_resource.h"  // IDC_HISTORY_MENU
+#import "chrome/browser/app_controller_mac.h"
 #include "chrome/browser/browser.h"
-#import "chrome/browser/cocoa/history_menu_cocoa_controller.h"
-#include "chrome/browser/browser_list.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/cocoa/event_utils.h"
 #include "chrome/browser/history/history.h"
@@ -25,6 +26,11 @@
   return self;
 }
 
+- (BOOL)validateMenuItem:(NSMenuItem*)menuItem {
+  AppController* controller = [NSApp delegate];
+  return [controller keyWindowIsNotModal];
+}
+
 // Open the URL of the given history item in the current tab.
 - (void)openURLForItem:(const HistoryMenuBridge::HistoryItem*)node {
   Browser* browser = Browser::GetOrCreateTabbedBrowser(bridge_->profile());