Implement contextmenu attribute with basic support of <menu>

Source/core/html/CustomContextMenuProvider.cpp

+// Copyright 2014 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 "config.h"
+#include "core/html/CustomContextMenuProvider.h"
+
+#include "core/dom/Document.h"
+#include "core/events/EventDispatcher.h"
+#include "core/events/MouseEvent.h"
+#include "core/html/HTMLMenuElement.h"
+#include "core/html/HTMLMenuItemElement.h"
+#include "platform/ContextMenu.h"
+
+namespace blink {
+
+CustomContextMenuProvider::CustomContextMenuProvider(HTMLMenuElement* menu, const Vector<ContextMenuItem>& items)
+    : m_menu(menu)
+    , m_items(items)
+{
+}
+
+CustomContextMenuProvider::~CustomContextMenuProvider()
+{
+}
+
+void CustomContextMenuProvider::populateContextMenu(ContextMenu* menu)
+{
+    for (size_t i = 0; i < m_items.size(); ++i)
+        menu->appendItem(m_items[i]);
+}
+
+void CustomContextMenuProvider::contextMenuItemSelected(const ContextMenuItem* item)
+{
+    if (!m_menu)

[tkent, 2014/07/25 04:42:37]

This check is unnecessary. m_menu is always non-null.

[pals, 2014/07/30 09:47:43]

This can happen if user has been shown context menu and js has removed the menu
from dom before selecting any item.

+        return;
+
+    if (HTMLMenuItemElement* element = m_menu->menuItemAt(item->action())) {
+        RefPtrWillBeRawPtr<SimulatedMouseEvent> click = SimulatedMouseEvent::create(EventTypeNames::click, m_menu->document().domWindow(), Event::create());

[tkent, 2014/07/25 04:42:37]

Why do you dispatch 'click' event even though the selection was done by keyboard
or something?

Do we need to pass Event::create()? Is passing null acceptable?

[pals, 2014/07/30 09:47:43]

Selection is done on menu shown by platform context menu, so we need to forward
this event by dispatching 'click'. 
Yes, we need to pass valid Event*.

[tkent, 2014/07/31 06:10:47]

I'm asking why 'click'.  We should not dispatch 'click' event for keyboard
operation.  Does the standard ask to dispatch 'click' event?

+        click->setRelatedTarget(m_menu->subjectElement());
+        EventDispatcher::dispatchEvent(element, EventDispatchMediator::create(click.release()));

[tkent, 2014/07/25 04:42:37]

Why don't you use element->dispatchEvent(click.release())?

[pals, 2014/07/30 09:47:43]

Done.

+    }
+}
+
+} // namespace blink