Bug 1870481 - Restore unified toolbar window looks. r=mac-reviewers,desktop-theme-reviewers,dao,spohl

By using a opaque-appearance widget (which is effectively what
appearance: -moz-dialog used to provide).

There's the question of whether we want the current vibrant titlebars,
but this restores the behavior precisely for now.

Differential Revision: https://phabricator.services.mozilla.com/D196712

browser/themes/osx/places/organizer.css

@@ -3,7 +3,8 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 :root {
-  background-color: transparent;
+  -moz-default-appearance: -moz-mac-unified-toolbar-window;
+  appearance: auto;
 }
 
 /* Places Organizer Sidebars */
@@ -34,7 +35,6 @@
 
 #placesView {
   border-top: none !important;
-  background-color: -moz-dialog;
 }
 
 #placesView > splitter {

browser/themes/shared/pageInfo.css

@@ -7,11 +7,8 @@
 
 @media (-moz-platform: macos) {
   :root {
-    background-color: transparent;
-  }
-
-  #mainDeck {
-    background-color: -moz-dialog;
+    -moz-default-appearance: -moz-mac-unified-toolbar-window;
+    appearance: auto;
   }
 
   #topBar {

servo/components/style/values/specified/box.rs

@@ -1648,6 +1648,12 @@ pub enum Appearance {
     #[parse(condition = "ParserContext::chrome_rules_enabled")]
     MozMacHelpButton,
 
+    /// An appearance value for the root, so that we can get unified toolbar looks (which require a
+    /// transparent gecko background) without really using the whole transparency set-up which
+    /// otherwise loses window borders, see bug 1870481.
+    #[parse(condition = "ParserContext::chrome_rules_enabled")]
+    MozMacUnifiedToolbarWindow,
+
     /// Windows themed window frame elements.
     #[parse(condition = "ParserContext::chrome_rules_enabled")]
     MozWindowButtonBox,

widget/cocoa/nsNativeThemeCocoa.mm

@@ -3172,6 +3172,7 @@ bool nsNativeThemeCocoa::ThemeSupportsWidget(nsPresContext* aPresContext,
     case StyleAppearance::MozMacHelpButton:
     case StyleAppearance::MozMacDisclosureButtonOpen:
     case StyleAppearance::MozMacDisclosureButtonClosed:
+    case StyleAppearance::MozMacUnifiedToolbarWindow:
     case StyleAppearance::Button:
     case StyleAppearance::Toolbarbutton:
     case StyleAppearance::Spinner:
@@ -3308,7 +3309,10 @@ nsITheme::Transparency nsNativeThemeCocoa::GetWidgetTransparency(
     case StyleAppearance::Tooltip:
     case StyleAppearance::Toolbar:
       return eTransparent;
-
+    case StyleAppearance::MozMacUnifiedToolbarWindow:
+      // We want these to be treated as opaque by Gecko. We ensure there's an
+      // appropriate OS-level clear color to make sure that's the case.
+      return eOpaque;
     case StyleAppearance::Statusbar:
       // Knowing that scrollbars and statusbars are opaque improves
       // performance, because we create layers for them.