Don't queue mutation records when attributes don't change value.

sky/tests/mutation-observer/observe-options-attributes.sky

Index: sky/tests/mutation-observer/observe-options-attributes.sky
diff --git a/sky/tests/mutation-observer/observe-options-attributes.sky b/sky/tests/mutation-observer/observe-options-attributes.sky
index b284bbb65470c1d10f2af291117ac8b2db95e153..db1f22bfda88f228d6a0a315a16c2b7f279cc0eb 100644
--- a/sky/tests/mutation-observer/observe-options-attributes.sky
+++ b/sky/tests/mutation-observer/observe-options-attributes.sky
@@ -9,21 +9,21 @@ describe('MutationObserver.observe', function() {
     element.setAttribute('data-test', '1');
 
     observer.observe(element, {attributeOldValue: true});
-    element.setAttribute('data-test', '1');
+    element.setAttribute('data-test', '2');
     var records = observer.takeRecords();
     assert.equal(records.length, 1);
     assert.equal(records[0].oldValue, 1);
     observer.disconnect();
 
     observer.observe(element, {attributeOldValue: false});
-    element.setAttribute('data-test', '1');
+    element.setAttribute('data-test', '3');
     var records = observer.takeRecords();
     assert.equal(records.length, 1);
     assert.isNull(records[0].oldValue);
     observer.disconnect();
 
     observer.observe(element, {attributeFilter: ['data-test']});
-    element.setAttribute('data-test', '2');
+    element.setAttribute('data-test', '4');
     var records = observer.takeRecords();
     assert.equal(records.length, 1);
     assert.isNull(records[0].oldValue);