Add the button style for combobox

ui/views/controls/menu/menu_runner.cc

Index: ui/views/controls/menu/menu_runner.cc
diff --git a/ui/views/controls/menu/menu_runner.cc b/ui/views/controls/menu/menu_runner.cc
index cc4f5022aee2f5081c7ce4f7742a31c6d69a364a..9033c20d811eabd607a188ae17e6f24155aa5b96 100644
--- a/ui/views/controls/menu/menu_runner.cc
+++ b/ui/views/controls/menu/menu_runner.cc
@@ -13,6 +13,7 @@
 #include "ui/views/controls/menu/menu_controller_delegate.h"
 #include "ui/views/controls/menu/menu_delegate.h"
 #include "ui/views/controls/menu/menu_model_adapter.h"
+#include "ui/views/controls/menu/menu_runner_core.h"
 #include "ui/views/widget/widget.h"
 
 #if defined(OS_WIN)
@@ -291,11 +292,13 @@ DisplayChangeListener* DisplayChangeListener::Create(Widget* widget,
 
 MenuRunner::MenuRunner(ui::MenuModel* menu_model)
     : menu_model_adapter_(new MenuModelAdapter(menu_model)),
-      holder_(new internal::MenuRunnerImpl(menu_model_adapter_->CreateMenu())) {
+      holder_(new internal::MenuRunnerImpl(menu_model_adapter_->CreateMenu())),
+      runner_core_(NULL) {
 }
 
 MenuRunner::MenuRunner(MenuItemView* menu)
-    : holder_(new internal::MenuRunnerImpl(menu)) {
+    : holder_(new internal::MenuRunnerImpl(menu)),
+      runner_core_(NULL) {
 }
 
 MenuRunner::~MenuRunner() {
@@ -312,6 +315,11 @@ MenuRunner::RunResult MenuRunner::RunMenuAt(Widget* parent,
                                             MenuItemView::AnchorPosition anchor,
                                             ui::MenuSourceType source_type,
                                             int32 types) {
+  if (runner_core_) {
+    return runner_core_->RunMenuAt(parent, button, bounds, anchor, source_type,
+                                   types);
+  }
+
   // The parent of the nested menu will have created a DisplayChangeListener, so
   // we avoid creating a DisplayChangeListener if nested. Drop menus are
   // transient, so we don't cancel in that case.