Bug 1707992 - Don't use native drawing for menupopups. r=stransky

It's not like our menupopups look anything like native ones other than
the color, anyways, so this will allow us to improve all our menupopups
at the same time.

Differential Revision: https://phabricator.services.mozilla.com/D113556

toolkit/themes/linux/global/popup.css

@@ -9,8 +9,7 @@
 
 menupopup,
 panel {
-  appearance: auto;
-  -moz-default-appearance: menupopup;
+  border: 1px solid ThreeDShadow;
   min-width: 1px;
   background-color: Menu;
   color: MenuText;
@@ -20,6 +19,7 @@ panel {
 
 panel[type="arrow"] {
   appearance: none;
+  border: none;
   background-color: transparent;
 }
 

widget/gtk/nsNativeThemeGTK.cpp

@@ -707,9 +707,6 @@ bool nsNativeThemeGTK::GetGtkWidgetAndState(StyleAppearance aAppearance,
     case StyleAppearance::Menubar:
       aGtkWidgetType = MOZ_GTK_MENUBAR;
       break;
-    case StyleAppearance::Menupopup:
-      aGtkWidgetType = MOZ_GTK_MENUPOPUP;
-      break;
     case StyleAppearance::Menuitem: {
       nsMenuFrame* menuFrame = do_QueryFrame(aFrame);
       if (menuFrame && menuFrame->IsOnMenuBar()) {
@@ -1679,7 +1676,6 @@ nsNativeThemeGTK::WidgetStateChanged(nsIFrame* aFrame,
       aAppearance == StyleAppearance::Progresschunk ||
       aAppearance == StyleAppearance::ProgressBar ||
       aAppearance == StyleAppearance::Menubar ||
-      aAppearance == StyleAppearance::Menupopup ||
       aAppearance == StyleAppearance::Tooltip ||
       aAppearance == StyleAppearance::Menuseparator) {
     *aShouldRepaint = false;
@@ -1853,7 +1849,6 @@ nsNativeThemeGTK::ThemeSupportsWidget(nsPresContext* aPresContext,
     case StyleAppearance::CheckboxLabel:
     case StyleAppearance::RadioLabel:
     case StyleAppearance::Menubar:
-    case StyleAppearance::Menupopup:
     case StyleAppearance::Menuitem:
     case StyleAppearance::Menuarrow:
     case StyleAppearance::Menuseparator:
@@ -1926,9 +1921,6 @@ bool nsNativeThemeGTK::ThemeNeedsComboboxDropmarker() { return false; }
 nsITheme::Transparency nsNativeThemeGTK::GetWidgetTransparency(
     nsIFrame* aFrame, StyleAppearance aAppearance) {
   switch (aAppearance) {
-    // These always draw a default background.
-    case StyleAppearance::Menupopup:
-      return eOpaque;
     case StyleAppearance::ScrollbarVertical:
     case StyleAppearance::ScrollbarHorizontal:
       // Make scrollbar tracks opaque on the window's scroll frame to prevent