Override CSSStyleDeclaration.getPropertyValue in general way.

lib/html/templates/html/impl/impl_CSSStyleDeclaration.darttemplate

Index: lib/html/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
diff --git a/lib/html/templates/html/impl/impl_CSSStyleDeclaration.darttemplate b/lib/html/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
index ddb804aef1c96e3fd1417fe1bef85d4fbac9a90d..c4c066dce24ae355b2126aad1e80e6ec1fa30009 100644
--- a/lib/html/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
+++ b/lib/html/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
@@ -23,16 +23,12 @@ class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 
 $!MEMBERS
 
-$if DART2JS
   String getPropertyValue(String propertyName) {
-    var propValue = JS('Object', '#.getPropertyValue(#)', this, propertyName);
-    if (propValue == null) {
-      return '';
-    } else {
-      return propValue;
-    }
+    var propValue = _getPropertyValue(propertyName);
+    return propValue != null ? propValue : '';
   }
 
+$if DART2JS
   void setProperty(String propertyName, String value, [String priority]) native '''
     this.setProperty(propertyName, value, priority);
     // Bug #2772, IE9 requires a poke to actually apply the value.