document.lastModified should consider user's local time zone

Source/core/html/shadow/DateTimeFieldElements.cpp

Index: Source/core/html/shadow/DateTimeFieldElements.cpp
diff --git a/Source/core/html/shadow/DateTimeFieldElements.cpp b/Source/core/html/shadow/DateTimeFieldElements.cpp
index 9479d9682bad28c8c0d131e518cd89853ede4922..530a9d226336c97e0c077dcf7dc8f934baa89e60 100644
--- a/Source/core/html/shadow/DateTimeFieldElements.cpp
+++ b/Source/core/html/shadow/DateTimeFieldElements.cpp
@@ -589,12 +589,7 @@ PassRefPtrWillBeRawPtr<DateTimeYearFieldElement> DateTimeYearFieldElement::creat
 
 static int currentFullYear()
 {
-    double current = currentTimeMS();
-    double utcOffset = calculateUTCOffset();
-    double dstOffset = calculateDSTOffset(current, utcOffset);
-    int offset = static_cast<int>((utcOffset + dstOffset) / msPerMinute);
-    current += offset * msPerMinute;
-
+    double current = convertToLocalTime(currentTimeMS());
     DateComponents date;
     date.setMillisecondsSinceEpochForMonth(current);
     return date.fullYear();