Syncing CssStyleDeclaration.setPropertyValue's signature between dart2js and dartium

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 94ee92e5598f0d56f02cf9cd3499cb18447b091b..0027a1d4342dbd1ae54fb4fc99df755c3a5d65d2 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -2172,9 +2172,13 @@ class CssStyleDeclaration native "CSSStyleDeclaration" {
     return propValue != null ? propValue : '';
   }
 
+  @DomName('CSSStyleDeclaration.setProperty')
   void setProperty(String propertyName, String value, [String priority]) {
     // try/catch for IE9 which throws on unsupported values.
     try {
+      if (priority == null) {
+        priority = '';
+      }
       JS('void', '#.setProperty(#, #, #)', this, propertyName, value, priority);
       // Bug #2772, IE9 requires a poke to actually apply the value.
       if (JS('bool', '!!#.setAttribute', this)) {