Clear mutable inline style when it is empty.

Source/core/dom/Element.h

Index: Source/core/dom/Element.h
diff --git a/Source/core/dom/Element.h b/Source/core/dom/Element.h
index bfc1d9afeab083839a28b8bb943f1217a29f3546..f1293c041634d78de827194f2903b95bd6b753c3 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -100,8 +100,11 @@ public:
 
     bool hasAttribute(const QualifiedName&) const;
     const AtomicString& getAttribute(const QualifiedName&) const;
+
+    // Passing nullAtom as the second parameter removes the attribute when calling either of these set methods.
     void setAttribute(const QualifiedName&, const AtomicString& value);
     void setSynchronizedLazyAttribute(const QualifiedName&, const AtomicString& value);
+
     void removeAttribute(const QualifiedName&);
 
     // Typed getters and setters for language bindings.
@@ -531,6 +534,7 @@ public:
     void synchronizeAttribute(const AtomicString& localName) const;
 
     MutableStylePropertySet* ensureMutableInlineStyle();
+    void clearMutableInlineStyleIfEmpty();
 
 protected:
     Element(const QualifiedName& tagName, Document* document, ConstructionType type)