Measure how often Attr needs its associated Element

Source/core/dom/Attr.cpp

Index: Source/core/dom/Attr.cpp
diff --git a/Source/core/dom/Attr.cpp b/Source/core/dom/Attr.cpp
index c6454fa4d863a4b31b85635fc15e37d60db963f3..08127695886e99964c2c08463ea3093b33ee069c 100644
--- a/Source/core/dom/Attr.cpp
+++ b/Source/core/dom/Attr.cpp
@@ -28,6 +28,7 @@
 #include "core/dom/Element.h"
 #include "core/dom/Text.h"
 #include "core/events/ScopedEventQueue.h"
+#include "core/frame/UseCounter.h"
 #include "wtf/text/AtomicString.h"
 #include "wtf/text/StringBuilder.h"
 
@@ -42,6 +43,7 @@ Attr::Attr(Element& element, const QualifiedName& name)
     , m_ignoreChildrenChanged(0)
 {
     ScriptWrappable::init(this);
+    m_standaloneValue = value();
 }
 
 Attr::Attr(Document& document, const QualifiedName& name, const AtomicString& standaloneValue)
@@ -94,8 +96,7 @@ void Attr::setValue(const AtomicString& value)
     removeChildren();
     if (m_element)
         elementAttribute().setValue(value);
-    else
-        m_standaloneValue = value;
+    m_standaloneValue = value;
     createTextChild();
     m_ignoreChildrenChanged--;
 
@@ -113,6 +114,20 @@ void Attr::setValue(const AtomicString& value, ExceptionState&)
         m_element->didModifyAttribute(qualifiedName(), value);
 }
 
+const AtomicString& Attr::valueForBindings() const
+{
+    if (m_element && m_standaloneValue != value())
+        UseCounter::count(document(), UseCounter::AttrGetValueNeedsElement);
+    return value();
+}
+
+void Attr::setValueForBindings(const AtomicString& value)
+{
+    if (m_element && value != this->value())
+        UseCounter::count(document(), UseCounter::AttrSetValueNeedsElement);
+    setValue(value, IGNORE_EXCEPTION);
+}
+
 void Attr::setNodeValue(const String& v)
 {
     // Attr uses AtomicString type for its value to save memory as there
@@ -138,6 +153,8 @@ void Attr::childrenChanged(bool, Node*, Node*, int)
     if (m_ignoreChildrenChanged > 0)
         return;
 
+    UseCounter::count(document(), UseCounter::AttrChildrenChanged);
+
     invalidateNodeListCachesInAncestors(&qualifiedName(), m_element);
 
     StringBuilder valueBuilder;
@@ -152,8 +169,7 @@ void Attr::childrenChanged(bool, Node*, Node*, int)
 
     if (m_element)
         elementAttribute().setValue(newValue);
-    else
-        m_standaloneValue = newValue;
+    m_standaloneValue = newValue;
 
     if (m_element)
         m_element->attributeChanged(qualifiedName(), newValue);
@@ -176,7 +192,6 @@ Attribute& Attr::elementAttribute()
 void Attr::detachFromElementWithValue(const AtomicString& value)
 {
     ASSERT(m_element);
-    ASSERT(m_standaloneValue.isNull());
     m_standaloneValue = value;
     m_element = 0;
 }
@@ -185,7 +200,7 @@ void Attr::attachToElement(Element* element)
 {
     ASSERT(!m_element);
     m_element = element;
-    m_standaloneValue = nullAtom;
+    m_standaloneValue = value();
 }
 
 }