Update documentation and cleanup impls for localToSVGParentTransform()

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

Index: third_party/WebKit/Source/core/layout/svg/LayoutSVGForeignObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/svg/LayoutSVGForeignObject.cpp b/third_party/WebKit/Source/core/layout/svg/LayoutSVGForeignObject.cpp
index 0457225f9d5283208d32a8a9ad263c9349ea93e9..2ca11e880e724b1ac207789438a70219fc2674cc 100644
--- a/third_party/WebKit/Source/core/layout/svg/LayoutSVGForeignObject.cpp
+++ b/third_party/WebKit/Source/core/layout/svg/LayoutSVGForeignObject.cpp
@@ -46,11 +46,11 @@ void LayoutSVGForeignObject::paint(const PaintInfo& paintInfo,
   SVGForeignObjectPainter(*this).paint(paintInfo);
 }
 
-const AffineTransform& LayoutSVGForeignObject::localToSVGParentTransform()
-    const {
-  m_localToParentTransform = localSVGTransform();
-  m_localToParentTransform.translate(m_viewport.x(), m_viewport.y());
-  return m_localToParentTransform;
+AffineTransform LayoutSVGForeignObject::localToSVGParentTransform() const {
+  // Unlike other viewport-defining SVG objects, here localSVGTransform applies
+  // to the viewport offset.
+  return localSVGTransform() *
+         AffineTransform::translation(m_viewport.x(), m_viewport.y());
 }
 
 void LayoutSVGForeignObject::updateLogicalWidth() {