Fix order of operations in LayoutView::mapAncestorToLocal

third_party/WebKit/Source/core/layout/LayoutView.cpp

Index: third_party/WebKit/Source/core/layout/LayoutView.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutView.cpp b/third_party/WebKit/Source/core/layout/LayoutView.cpp
index 049640447983c0360c72adfea4309b6aedcde362..ee065145857401b902663ddf47449fee1ec4c1f6 100644
--- a/third_party/WebKit/Source/core/layout/LayoutView.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutView.cpp
@@ -375,28 +375,20 @@ void LayoutView::mapAncestorToLocal(const LayoutBoxModelObject* ancestor, Transf
     if (this == ancestor)
         return;
 
-    if (mode & IsFixed && m_frameView)
-        transformState.move(m_frameView->scrollOffset());
-
-    if (mode & UseTransforms && shouldUseTransformFromContainer(0)) {
-        TransformationMatrix t;
-        getTransformFromContainer(0, LayoutSize(), t);
-        transformState.applyTransform(t);
-    }
-
     if (mode & TraverseDocumentBoundaries) {
         if (LayoutPart* parentDocLayoutObject = frame()->ownerLayoutObject()) {
-            // A LayoutView is a containing block for fixed-position elements, so don't carry this state across frames.
-            mode &= ~IsFixed;
+            parentDocLayoutObject->mapAncestorToLocal(ancestor, transformState, mode & ~IsFixed);
 
-            transformState.move(-frame()->view()->scrollOffset());
+            // A LayoutView is a containing block for fixed-position elements, so don't carry this state across frames.

[Xianzhu, 2016/07/14 17:40:11]

Move this comment to above line 380.

[chrishtr, 2016/07/28 16:21:13]

Done.

             transformState.move(parentDocLayoutObject->contentBoxOffset());
-
-            parentDocLayoutObject->mapAncestorToLocal(ancestor, transformState, mode);
+            transformState.move(-frame()->view()->scrollOffset());

[Xianzhu, 2016/07/14 17:40:11]

Can this be:
   if (!(mode & IsFixed))
      transformState.move(-frame()->view()->scrollOffset());
   return;
to avoid moving back and forth for fixed?

[chrishtr, 2016/07/28 16:21:13]

I could, but then I would have to add an else clause if
TraverseDocumentBoundaries was false.

         }
     } else {
         ASSERT(!ancestor);
     }
+
+    if (mode & IsFixed)
+        transformState.move(frame()->view()->scrollOffset());
 }
 
 void LayoutView::computeSelfHitTestRects(Vector<LayoutRect>& rects, const LayoutPoint&) const