[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::kMenuActivationAction);
+    set_request_focus_on_press(true);

[tapted, 2016/06/22 04:23:03]

oh hang on a sec.. I just noticed the OnMousePressed override does
*parent()*->RequestFocus but that's not what set_request_focus_on_press will do
- doh.

So I think we need to keep that override. But:

- with the RequestFocus() call between #if defined(OS_MACOSX)
- with the call to super::OnMousePressed

   }
   ~TransparentButton() override {}
 
-  bool OnMousePressed(const ui::MouseEvent& mouse_event) override {
-    parent()->RequestFocus();
-    return true;
-  }
-
   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).
 // Skips separator or disabled indices. Returns -1 if there is no valid adjacent
@@ skipping 763 matching lines @@
 }
 
 int Combobox::GetArrowContainerWidth() const {
   int padding = style_ == STYLE_NORMAL
                     ? PlatformStyle::kComboboxNormalArrowPadding * 2
                     : kActionLeftPadding + kActionRightPadding;
   return ArrowSize().width() + padding;
 }
 
 }  // namespace views