[MacViews] Show combobox menu popup at mouse press

ui/views/controls/combobox/combobox.cc

Index: ui/views/controls/combobox/combobox.cc
diff --git a/ui/views/controls/combobox/combobox.cc b/ui/views/controls/combobox/combobox.cc
index 3d7cfd1e26585dae22ab9fd8f8cfe5d876987304..51fcbe3a745fbf0bc211c9cc3c95d343d170f6c6 100644
--- a/ui/views/controls/combobox/combobox.cc
+++ b/ui/views/controls/combobox/combobox.cc
@@ -110,14 +110,11 @@ class TransparentButton : public CustomButton {
       : 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();
   }