Revert of Remove FrameView::Root

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index 88a748f593e1d184af203fc18e5c96b5a3e37a52..0a34de2ebdd1c72b5513d2132c2bb5ad3adfcc90 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -3849,6 +3849,13 @@
   animating_scrollable_areas_->erase(scrollable_area);
 }
 
+FrameView* FrameView::Root() const {
+  const FrameView* top = this;
+  while (top->Parent())
+    top = ToFrameView(top->Parent());
+  return const_cast<FrameView*>(top);
+}
+
 void FrameView::SetParent(FrameViewBase* parent_frame_view_base) {
   FrameView* parent = ToFrameView(parent_frame_view_base);
   if (parent == parent_)