Don't force-update style and layout in Document::scrollingElement

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index f42226205775d7df98216f125d44c20a63f005cc..bb7fa1e5091a70a720fe9b6407e4ec3930f6e6ee 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -1345,9 +1345,15 @@ Range* Document::caretRangeFromPoint(int x, int y) {
 }
 
 Element* Document::scrollingElement() {
+  if (RuntimeEnabledFeatures::scrollTopLeftInteropEnabled() && inQuirksMode())
+    updateStyleAndLayoutTree();
+  return scrollingElementNoLayout();
+}
+
+Element* Document::scrollingElementNoLayout() {
   if (RuntimeEnabledFeatures::scrollTopLeftInteropEnabled()) {
     if (inQuirksMode()) {
-      updateStyleAndLayoutTree();
+      DCHECK(m_lifecycle.state() >= DocumentLifecycle::StyleClean);

[chrishtr, 2017/01/11 17:19:00]

StyleClean is the right one, since updateStyleAndLayoutTree()
does not layout, just updates style and creates the layout tree.

       HTMLBodyElement* body = firstBodyElement();
       if (body && body->layoutObject() &&
           body->layoutObject()->hasOverflowClip())