[ash] Add TYPE_DIALOG and its item's LauncherContextMenu

This is third CL for adding an item for dialog.
This cl adds new LauncherItemType, TYPE_DIALOG, and 
implements a context menu of item created by ShelfWindowWatcher.

[email protected]
BUG=121242
TEST=NONE

Review URL: https://codereview.chromium.org/107163005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243965 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index ab41a4c..20e8fde 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -158,7 +158,10 @@
   return NULL;
 }
 
-ui::MenuModel* ShellDelegateImpl::CreateContextMenu(aura::Window* root) {
+ui::MenuModel* ShellDelegateImpl::CreateContextMenu(
+    aura::Window* root,
+    ash::ShelfItemDelegate* item_delegate,
+    ash::LauncherItem* item) {
   return new ContextMenu(root);
 }