Make sure getAttribute() / setAttribute() callers use AtomicStrings

Source/core/page/EventHandler.cpp

Index: Source/core/page/EventHandler.cpp
diff --git a/Source/core/page/EventHandler.cpp b/Source/core/page/EventHandler.cpp
index 9a7a8bcb36c5e0f83a7f949f878953f303e0eab3..d7824a8407acb30b6b96a556d3dae849415bcd5c 100644
--- a/Source/core/page/EventHandler.cpp
+++ b/Source/core/page/EventHandler.cpp
@@ -1776,7 +1776,7 @@ static bool findDropZone(Node* target, Clipboard* clipboard)
     Element* element = target->isElementNode() ? toElement(target) : target->parentElement();
     for (; element; element = element->parentElement()) {
         bool matched = false;
-        String dropZoneStr = element->fastGetAttribute(webkitdropzoneAttr);
+        AtomicString dropZoneStr = element->fastGetAttribute(webkitdropzoneAttr);
 
         if (dropZoneStr.isEmpty())
             continue;