Bug 1833466 - Implement CSSMarginRule and the corresponding DOM API. r=webidl,firefox-style-system-reviewers,smaug,emilio

Differential Revision: https://phabricator.services.mozilla.com/D206804

layout/style/ServoStyleSet.cpp

@@ -34,6 +34,7 @@
 #include "mozilla/dom/CSSContainerRule.h"
 #include "mozilla/dom/CSSLayerBlockRule.h"
 #include "mozilla/dom/CSSLayerStatementRule.h"
+#include "mozilla/dom/CSSMarginRule.h"
 #include "mozilla/dom/CSSMediaRule.h"
 #include "mozilla/dom/CSSMozDocumentRule.h"
 #include "mozilla/dom/CSSKeyframesRule.h"
@@ -994,6 +995,7 @@ void ServoStyleSet::RuleChangedInternal(StyleSheet& aSheet, css::Rule& aRule,
     CASE_FOR(Import, Import)
     CASE_FOR(Media, Media)
     CASE_FOR(Keyframes, Keyframes)
+    CASE_FOR(Margin, Margin)
     CASE_FOR(FontFeatureValues, FontFeatureValues)
     CASE_FOR(FontPaletteValues, FontPaletteValues)
     CASE_FOR(FontFace, FontFace)
@@ -1014,9 +1016,6 @@ void ServoStyleSet::RuleChangedInternal(StyleSheet& aSheet, css::Rule& aRule,
       // FIXME: We should probably just forward to the parent @keyframes rule? I
       // think that'd do the right thing, but meanwhile...
       return MarkOriginsDirty(ToOriginFlags(aSheet.GetOrigin()));
-    case StyleCssRuleType::Margin:
-      // Margin rules not implemented yet, see bug 1864737
-      break;
   }
 
 #undef CASE_FOR