Use new is*Element() helper functions more in core/ code

Source/core/frame/SmartClip.cpp

Index: Source/core/frame/SmartClip.cpp
diff --git a/Source/core/frame/SmartClip.cpp b/Source/core/frame/SmartClip.cpp
index bffd99761aec5a0e216a5a9056b264699ddd2333..3a95095c06e4ef057ba19fe6b31f9962b2223556 100644
--- a/Source/core/frame/SmartClip.cpp
+++ b/Source/core/frame/SmartClip.cpp
@@ -221,8 +221,9 @@ Node* SmartClip::findBestOverlappingNode(Node* rootNode, const IntRect& cropRect
 // CSS background images but to skip actual backgrounds.
 bool SmartClip::shouldSkipBackgroundImage(Node* node)
 {
+    ASSERT(node);
     // Apparently we're only interested in background images on spans and divs.
-    if (!node->hasTagName(HTMLNames::spanTag) && !node->hasTagName(HTMLNames::divTag))
+    if (!isHTMLSpanElement(*node) && !isHTMLDivElement(*node))
         return true;
 
     // This check actually makes a bit of sense. If you're going to sprite an