Drop const_iterator for AttributeCollection

Source/web/WebPageSerializerImpl.cpp

Index: Source/web/WebPageSerializerImpl.cpp
diff --git a/Source/web/WebPageSerializerImpl.cpp b/Source/web/WebPageSerializerImpl.cpp
index 45b1381ca8c2ba2efc76ae3576dbbbaa8a1516be..cb1321de8283b22f29d0bc3398723fb2a0054019 100644
--- a/Source/web/WebPageSerializerImpl.cpp
+++ b/Source/web/WebPageSerializerImpl.cpp
@@ -303,8 +303,8 @@ void WebPageSerializerImpl::openTagToString(Element* element,
     result.append(element->nodeName().lower());
     // Go through all attributes and serialize them.
     AttributeCollection attributes = element->attributes();
-    AttributeCollection::const_iterator end = attributes.end();
-    for (AttributeCollection::const_iterator it = attributes.begin(); it != end; ++it) {
+    AttributeCollection::iterator end = attributes.end();
+    for (AttributeCollection::iterator it = attributes.begin(); it != end; ++it) {
         result.append(' ');
         // Add attribute pair
         result.append(it->name().toString());