[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 dc7797936b73c56c043e2d2873986603ab04804f..2792505b826752d8f87119b3590924fddc401056 100644
--- a/ui/views/controls/combobox/combobox.cc
+++ b/ui/views/controls/combobox/combobox.cc
@@ -110,11 +110,13 @@ class TransparentButton : public CustomButton {
       : CustomButton(listener) {
     SetAnimationDuration(LabelButton::kHoverAnimationDurationMs);
     SetFocusBehavior(FocusBehavior::NEVER);
+    set_notify_action(NOTIFY_ON_PRESS);

[tapted, 2016/06/16 00:05:13]

We need to restrict this just to Mac - I think the way to go about it is to add

CustomButton::NotifyAction PlatformStyle::kMenuActivationAction =
CustomButton::NOTIFY_ON_PRESS;

in platform_style_mac.mm

(and = CustomButton::NOTIFY_ON_RELEASE in platform_style.cc within the !mac
guards)

[spqchan, 2016/06/22 02:16:38]

Done.

   }
   ~TransparentButton() override {}
 
   bool OnMousePressed(const ui::MouseEvent& mouse_event) override {
     parent()->RequestFocus();

[tapted, 2016/06/16 00:05:13]

This actually isn't needed, CustomButton has a set_request_focus_on_press(bool)
method which TransparentButton can call in the constructor.

Conveniently, that setter is disabled on Mac - and that's exactly what we want,
since activating a native combobox doesn't transfer focus to the combobox
control.

So I think we can get rid of the OnMousePressed override completely (regardless
of platform) by adding that set_request_focus_on_press call

(make sure you say something about this in the CL description, since it's
subtle)

[spqchan, 2016/06/22 02:16:38]

Done.

+    CustomButton::OnMousePressed(mouse_event);
     return true;
   }