[Blending and compositing] Implement the isolation CSS property in software

Source/core/rendering/style/RenderStyle.cpp

Index: Source/core/rendering/style/RenderStyle.cpp
diff --git a/Source/core/rendering/style/RenderStyle.cpp b/Source/core/rendering/style/RenderStyle.cpp
index 121dd88c19706da2ea9d7ce76844807581b22d43..d5ef0efec30071851836ad57537ada43447a080e 100644
--- a/Source/core/rendering/style/RenderStyle.cpp
+++ b/Source/core/rendering/style/RenderStyle.cpp
@@ -835,6 +835,13 @@ void RenderStyle::setIsolation(EIsolation v)
         rareNonInheritedData.access()->m_isolation = v;
 }
 
+bool RenderStyle::hasIsolation() const
+{
+    if (RuntimeEnabledFeatures::cssCompositingEnabled())
+        return rareNonInheritedData->m_isolation != IsolationAuto;
+    return false;
+}
+
 inline bool requireTransformOrigin(const Vector<RefPtr<TransformOperation> >& transformOperations, RenderStyle::ApplyTransformOrigin applyOrigin)
 {
     // transform-origin brackets the transform with translate operations.