Add back CssCharsetRule for Safari support

tools/dom/idl/dart/dart.idl

Index: tools/dom/idl/dart/dart.idl
diff --git a/tools/dom/idl/dart/dart.idl b/tools/dom/idl/dart/dart.idl
index 0014a1b0a29da1a7d2d3159ef89aae47a1474ca5..533a448b4caa60f581143c154709aa08a90a0f5e 100644
--- a/tools/dom/idl/dart/dart.idl
+++ b/tools/dom/idl/dart/dart.idl
@@ -423,3 +423,10 @@ interface MIDIOutput : MIDIPort {
 };
 
 Element implements GlobalEventHandlers;
+
+
+// This only exists in Safari, and is deprecated there. But include it anyway
+// because otherwise iterating CSSRules in Safari can yield unknown JS objects.
+interface CSSCharsetRule : CSSRule {
+    [MeasureAs=CSSCharsetRuleEncoding] attribute DOMString encoding;
+};