[MacViews] Show combobox menu popup at mouse press

ui/views/controls/combobox/combobox.cc

 // Copyright (c) 2012 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/controls/combobox/combobox.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 92 matching lines @@
   return bounds;
 }
 
 // The transparent button which holds a button state but is not rendered.
 class TransparentButton : public CustomButton {
  public:
   TransparentButton(ButtonListener* listener)
       : CustomButton(listener) {
     SetAnimationDuration(LabelButton::kHoverAnimationDurationMs);
     SetFocusBehavior(FocusBehavior::NEVER);
+    set_notify_action(PlatformStyle::kMenuNotifyActivationAction);
   }
   ~TransparentButton() override {}
 
+#if !defined(OS_MACOSX)
+  // Override OnMousePressed() to transfer focus to the parent() on a click
+  // except on Mac, which doesn't transfer focus when buttons are clicked.
   bool OnMousePressed(const ui::MouseEvent& mouse_event) override {
     parent()->RequestFocus();
     return true;
   }
+#endif
 
   double GetAnimationValue() const {
     return hover_animation().GetCurrentValue();
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TransparentButton);
 };
 
 // Returns the next or previous valid index (depending on |increment|'s value).
@@ skipping 764 matching lines @@
 }
 
 int Combobox::GetArrowContainerWidth() const {
   int padding = style_ == STYLE_NORMAL
                     ? PlatformStyle::kComboboxNormalArrowPadding * 2
                     : kActionLeftPadding + kActionRightPadding;
   return ArrowSize().width() + padding;
 }
 
 }  // namespace views