Do not commit: Revert of r404081 and r402757 for perf testing purposes.

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

Index: third_party/WebKit/Source/core/layout/LayoutObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.cpp b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
index 78d02a87c11a1c59fab1f61efe381b2dd8aebd62..4f4997278c8b7b0c4a1a1260574944a6c6d2bfb8 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -3213,12 +3213,12 @@ void LayoutObject::imageChanged(ImageResource* image, const IntRect* rect)
     imageChanged(static_cast<WrappedImagePtr>(image), rect);
 }
 
-Element* LayoutObject::offsetParent(const Element* unclosedBase) const
+Element* LayoutObject::offsetParent() const
 {
     if (isDocumentElement() || isBody())
         return nullptr;
 
-    if (isFixedPositioned())
+    if (isOutOfFlowPositioned() && style()->position() == FixedPosition)
         return nullptr;
 
     float effectiveZoom = style()->effectiveZoom();
@@ -3231,16 +3231,6 @@ Element* LayoutObject::offsetParent(const Element* unclosedBase) const
         if (!node)
             continue;
 
-        // TODO(kochi): If |unclosedBase| or |node| is nested deep in shadow roots, this loop may
-        // get expensive, as isUnclosedNodeOf() can take up to O(N+M) time (N and M are depths).
-        if (unclosedBase && (!node->isUnclosedNodeOf(*unclosedBase) || (node->isInShadowTree() && node->containingShadowRoot()->type() == ShadowRootType::UserAgent))) {
-            // If 'position: fixed' node is found while traversing up, terminate the loop and
-            // return null.
-            if (ancestor->isFixedPositioned())
-                return nullptr;
-            continue;
-        }
-
         if (ancestor->isPositioned())
             break;