style: Make modal dialog code more generic, and make it apply to full…

…screen too behind a pref

For now, don't turn it on by default yet, because I want to wait for
more discussion in w3c/csswg-drafts#6965 and
so on. But I think the code is simple enough to land this.

Differential Revision: https://phabricator.services.mozilla.com/D147295

components/style/element_state.rs

@@ -118,8 +118,8 @@ bitflags! {
         const IN_MODAL_DIALOG_STATE = 1 << 42;
         /// <https://html.spec.whatwg.org/multipage/#inert-subtrees>
         const IN_MOZINERT_STATE = 1 << 43;
-        /// State for the topmost dialog element in top layer
-        const IN_TOPMOST_MODAL_DIALOG_STATE = 1 << 44;
+        /// State for the topmost modal element in top layer
+        const IN_TOPMOST_MODAL_TOP_LAYER_STATE = 1 << 44;
         /// Initially used for the devtools highlighter, but now somehow only
         /// used for the devtools accessibility inspector.
         const IN_DEVTOOLS_HIGHLIGHTED_STATE = 1 << 45;

components/style/gecko/non_ts_pseudo_class_list.rs

@@ -54,7 +54,7 @@ macro_rules! apply_non_ts_list {
                 ("-moz-styleeditor-transitioning", MozStyleeditorTransitioning, IN_STYLEEDITOR_TRANSITIONING_STATE, PSEUDO_CLASS_ENABLED_IN_UA_SHEETS),
                 ("fullscreen", Fullscreen, IN_FULLSCREEN_STATE, _),
                 ("-moz-modal-dialog", MozModalDialog, IN_MODAL_DIALOG_STATE, PSEUDO_CLASS_ENABLED_IN_UA_SHEETS),
-                ("-moz-topmost-modal-dialog", MozTopmostModalDialog, IN_TOPMOST_MODAL_DIALOG_STATE, PSEUDO_CLASS_ENABLED_IN_UA_SHEETS),
+                ("-moz-topmost-modal", MozTopmostModal, IN_TOPMOST_MODAL_TOP_LAYER_STATE, PSEUDO_CLASS_ENABLED_IN_UA_SHEETS),
                 ("-moz-broken", MozBroken, IN_BROKEN_STATE, _),
                 ("-moz-loading", MozLoading, IN_LOADING_STATE, _),
                 ("-moz-has-dir-attr", MozHasDirAttr, IN_HAS_DIR_ATTR_STATE, PSEUDO_CLASS_ENABLED_IN_UA_SHEETS),

components/style/gecko/wrapper.rs

@@ -2006,7 +2006,7 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
             NonTSPseudoClass::MozDirAttrRTL |
             NonTSPseudoClass::MozDirAttrLikeAuto |
             NonTSPseudoClass::MozModalDialog |
-            NonTSPseudoClass::MozTopmostModalDialog |
+            NonTSPseudoClass::MozTopmostModal |
             NonTSPseudoClass::Active |
             NonTSPseudoClass::Hover |
             NonTSPseudoClass::MozAutofillPreview |