Avoid using forced layout to trigger paint invalidation for SVG containers

third_party/WebKit/Source/core/layout/svg/LayoutSVGTransformableContainer.cpp

Index: third_party/WebKit/Source/core/layout/svg/LayoutSVGTransformableContainer.cpp
diff --git a/third_party/WebKit/Source/core/layout/svg/LayoutSVGTransformableContainer.cpp b/third_party/WebKit/Source/core/layout/svg/LayoutSVGTransformableContainer.cpp
index e27c088da31d36a9f684c06e4d686ed8ec29f84d..3c7b70ca1ad1194c04ae01d532c56181c2212d12 100644
--- a/third_party/WebKit/Source/core/layout/svg/LayoutSVGTransformableContainer.cpp
+++ b/third_party/WebKit/Source/core/layout/svg/LayoutSVGTransformableContainer.cpp
@@ -66,7 +66,18 @@ bool LayoutSVGTransformableContainer::isChildAllowed(LayoutObject* child, const
     return LayoutSVGContainer::isChildAllowed(child, style);
 }
 
-bool LayoutSVGTransformableContainer::calculateLocalTransform()
+void LayoutSVGTransformableContainer::setNeedsTransformUpdate()
+{
+    setMayNeedPaintInvalidationSubtree();
+    m_needsTransformUpdate = true;
+}
+
+static std::pair<double, double> scaleReference(const AffineTransform& transform)
+{
+    return std::make_pair(transform.xScaleSquared(), transform.yScaleSquared());
+}
+
+LayoutSVGContainer::TransformChange LayoutSVGTransformableContainer::calculateLocalTransform()
 {
     SVGGraphicsElement* element = toSVGGraphicsElement(this->element());
     ASSERT(element);
@@ -88,18 +99,23 @@ bool LayoutSVGTransformableContainer::calculateLocalTransform()
         FloatSize translation(
             useElement->x()->currentValue()->value(lengthContext),
             useElement->y()->currentValue()->value(lengthContext));
+        // TODO(fs): Signal this on style update instead. (Since these are
+        // suppose to be presentation attributes now, this does feel a bit
+        // broken...)
         if (translation != m_additionalTranslation)
-            m_needsTransformUpdate = true;
+            setNeedsTransformUpdate();
         m_additionalTranslation = translation;
     }
 
     if (!m_needsTransformUpdate)
-        return false;
+        return TransformChange::None;
 
+    std::pair<double, double> oldScale = scaleReference(m_localTransform);
     m_localTransform = element->calculateAnimatedLocalTransform();
     m_localTransform.translate(m_additionalTranslation.width(), m_additionalTranslation.height());
     m_needsTransformUpdate = false;
-    return true;
+    return scaleReference(m_localTransform) != oldScale
+        ? TransformChange::Full : TransformChange::ScaleInvariant;
 }
 
 } // namespace blink