Add back CssCharsetRule for Safari support

sdk/lib/_blink/dartium/_blink_dartium.dart

Index: sdk/lib/_blink/dartium/_blink_dartium.dart
diff --git a/sdk/lib/_blink/dartium/_blink_dartium.dart b/sdk/lib/_blink/dartium/_blink_dartium.dart
index 1cd44aaa9dbe4ed7d2bcdf6d7e911a33563bfffa..37471b9a1ce1c184a443918c2787ddc1f3d1d3bb 100644
--- a/sdk/lib/_blink/dartium/_blink_dartium.dart
+++ b/sdk/lib/_blink/dartium/_blink_dartium.dart
@@ -60,6 +60,7 @@ dynamic resolver(String s) {
   if (s == "CHROMIUMSubscribeUniform") return BlinkCHROMIUMSubscribeUniform.instance;
   if (s == "CHROMIUMValuebuffer") return BlinkCHROMIUMValuebuffer.instance;
   if (s == "CSS") return BlinkCSS.instance;
+  if (s == "CSSCharsetRule") return BlinkCSSCharsetRule.instance;
   if (s == "CSSFontFaceRule") return BlinkCSSFontFaceRule.instance;
   if (s == "CSSGroupingRule") return BlinkCSSGroupingRule.instance;
   if (s == "CSSImportRule") return BlinkCSSImportRule.instance;
@@ -1716,6 +1717,15 @@ class BlinkCSS {
 
 }
 
+class BlinkCSSCharsetRule extends BlinkCSSRule {
+  static final instance = new BlinkCSSCharsetRule();
+
+  encoding_Getter_(mthis) => Blink_JsNative_DomException.getProperty(mthis, "encoding");
+
+  encoding_Setter_(mthis, __arg_0) => mthis["encoding"] = __arg_0;
+
+}
+
 class BlinkCSSFontFaceRule extends BlinkCSSRule {
   static final instance = new BlinkCSSFontFaceRule();