Share inline style between cloned Nodes (copy on write.)

<http://webkit.org/b/95451>

Reviewed by Antti Koivisto.

When cloning a Node, use an immutable StylePropertySet for the new Node's inline style.
If the old Node already had an immutable inline style, we now reuse that, avoiding a copy.
Copying is deferred until mutation (either via CSSOM or setting of the style attribute.)

* dom/ElementAttributeData.cpp:
(WebCore::ElementAttributeData::cloneDataFrom):
* css/StylePropertySet.h:
* css/StylePropertySet.cpp:
(WebCore::StylePropertySet::immutableCopyIfNeeded):

    Added. Simply returns 'this' if the object is already immutable, otherwise creates a new one.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@127375 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebCore/ChangeLog

@@ -1,3 +1,22 @@
+2012-09-01  Andreas Kling  <kling@webkit.org>
+
+        Share inline style between cloned Nodes (copy on write.)
+        <http://webkit.org/b/95451>
+
+        Reviewed by Antti Koivisto.
+
+        When cloning a Node, use an immutable StylePropertySet for the new Node's inline style.
+        If the old Node already had an immutable inline style, we now reuse that, avoiding a copy.
+        Copying is deferred until mutation (either via CSSOM or setting of the style attribute.)
+
+        * dom/ElementAttributeData.cpp:
+        (WebCore::ElementAttributeData::cloneDataFrom):
+        * css/StylePropertySet.h:
+        * css/StylePropertySet.cpp:
+        (WebCore::StylePropertySet::immutableCopyIfNeeded):
+
+            Added. Simply returns 'this' if the object is already immutable, otherwise creates a new one.
+
 2012-09-01  Dirk Schulze  <krit@webkit.org>
 
         [Qt] Fix the --minimal build after r127327

Source/WebCore/css/StylePropertySet.cpp

@@ -61,6 +61,13 @@ PassRefPtr<StylePropertySet> StylePropertySet::createImmutable(const CSSProperty
     return adoptRef(new (slot) StylePropertySet(properties, count, cssParserMode, /* makeMutable */ false));
 }
 
+PassRefPtr<StylePropertySet> StylePropertySet::immutableCopyIfNeeded() const
+{
+    if (!isMutable())
+        return const_cast<StylePropertySet*>(this);
+    return createImmutable(m_mutablePropertyVector->data(), m_mutablePropertyVector->size(), cssParserMode());
+}
+
 StylePropertySet::StylePropertySet(CSSParserMode cssParserMode)
     : m_cssParserMode(cssParserMode)
     , m_ownsCSSOMWrapper(false)

Source/WebCore/css/StylePropertySet.h

@@ -91,6 +91,7 @@ class StylePropertySet : public RefCounted<StylePropertySet> {
     void addSubresourceStyleURLs(ListHashSet<KURL>&, StyleSheetContents* contextStyleSheet) const;
 
     PassRefPtr<StylePropertySet> copy() const;
+    PassRefPtr<StylePropertySet> immutableCopyIfNeeded() const;
 
     void removeEquivalentProperties(const StylePropertySet*);
     void removeEquivalentProperties(const CSSStyleDeclaration*);

Source/WebCore/dom/ElementAttributeData.cpp

@@ -363,7 +363,7 @@ void ElementAttributeData::cloneDataFrom(const ElementAttributeData& sourceData,
     }
 
     if (targetElement.isStyledElement() && sourceData.m_inlineStyleDecl) {
-        m_inlineStyleDecl = sourceData.m_inlineStyleDecl->copy();
+        m_inlineStyleDecl = sourceData.m_inlineStyleDecl->immutableCopyIfNeeded();
         targetElement.setIsStyleAttributeValid(sourceElement.isStyleAttributeValid());
     }
 }