Guard the rework of documentElement|body.scrollTop/Left under a runtime flag

Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 659 matching lines @@
 
     if (RenderBox* renderer = renderBox())
         return adjustLayoutUnitForAbsoluteZoom(renderer->pixelSnappedClientHeight(), *renderer).round();
     return 0;
 }
 
 int Element::scrollLeft()
 {
     document().updateLayoutIgnorePendingStylesheets();
 
-    if (document().documentElement() == this) {
+    if (document().documentElement() != this) {
+        if (RenderBox* rend = renderBox())
+            return adjustForAbsoluteZoom(rend->scrollLeft(), rend);
+        return 0;
+    }
+
+    if (RuntimeEnabledFeatures::scrollTopLeftInteropEnabled()) {
         if (document().inQuirksMode())
             return 0;
 
         if (FrameView* view = document().view()) {
             if (RenderView* renderView = document().renderView())
                 return adjustForAbsoluteZoom(view->scrollX(), renderView);
         }
     }
 
-    if (RenderBox* rend = renderBox())
-        return adjustForAbsoluteZoom(rend->scrollLeft(), rend);
     return 0;
 }
 
 int Element::scrollTop()
 {
     document().updateLayoutIgnorePendingStylesheets();
 
-    if (document().documentElement() == this) {
+    if (document().documentElement() != this) {
+        if (RenderBox* rend = renderBox())
+            return adjustForAbsoluteZoom(rend->scrollTop(), rend);
+        return 0;
+    }
+
+    if (RuntimeEnabledFeatures::scrollTopLeftInteropEnabled()) {
         if (document().inQuirksMode())
             return 0;
 
         if (FrameView* view = document().view()) {
             if (RenderView* renderView = document().renderView())
                 return adjustForAbsoluteZoom(view->scrollY(), renderView);
         }
     }
 
-    if (RenderBox* rend = renderBox())
-        return adjustForAbsoluteZoom(rend->scrollTop(), rend);
     return 0;
 }
 
 void Element::setScrollLeft(int newLeft)
 {
     document().updateLayoutIgnorePendingStylesheets();
 
-    if (document().documentElement() == this) {
+    if (document().documentElement() != this) {
+        if (RenderBox* rend = renderBox())
+            rend->setScrollLeft(static_cast<int>(newLeft * rend->style()->effectiveZoom()));
+        return;
+    }
+
+    if (RuntimeEnabledFeatures::scrollTopLeftInteropEnabled()) {
         if (document().inQuirksMode())
             return;
 
         Frame* frame = document().frame();
         if (!frame)
             return;
         FrameView* view = frame->view();
         if (!view)
             return;
 
-        // WHATWG spec says [1]: "If the element is the root element invoke scroll()
-        // with x as first argument and zero as second". Blink intentionally matches
-        // other engine's behaviors here, instead, where the 'y' scroll position is
-        // preversed. See [2].
-        // [1] http://dev.w3.org/csswg/cssom-view/#dom-element-scrollleft
-        // [2] https://www.w3.org/Bugs/Public/show_bug.cgi?id=23448
         view->setScrollPosition(IntPoint(static_cast<int>(newLeft * frame->pageZoomFactor()), view->scrollY()));
     }
-
-    if (RenderBox* rend = renderBox())
-        rend->setScrollLeft(static_cast<int>(newLeft * rend->style()->effectiveZoom()));
 }
 
 void Element::setScrollTop(int newTop)
 {
     document().updateLayoutIgnorePendingStylesheets();
 
-    if (document().documentElement() == this) {
+    if (document().documentElement() != this) {
+        if (RenderBox* rend = renderBox())
+            rend->setScrollTop(static_cast<int>(newTop * rend->style()->effectiveZoom()));
+        return;
+    }
+
+    if (RuntimeEnabledFeatures::scrollTopLeftInteropEnabled()) {
         if (document().inQuirksMode())
             return;
 
         Frame* frame = document().frame();
         if (!frame)
             return;
         FrameView* view = frame->view();
         if (!view)
             return;
 
-        // WHATWG spec says [1]: "If the element is the root element invoke scroll()
-        // with zero as first argument and y as second". Blink intentionally
-        // matches other engine's behaviors here, instead, where the 'x' scroll
-        // position is preversed. See [2].
-        // [1] http://dev.w3.org/csswg/cssom-view/#dom-element-scrolltop
-        // [2] https://www.w3.org/Bugs/Public/show_bug.cgi?id=23448
         view->setScrollPosition(IntPoint(view->scrollX(), static_cast<int>(newTop * frame->pageZoomFactor())));
     }
-
-    if (RenderBox* rend = renderBox())
-        rend->setScrollTop(static_cast<int>(newTop * rend->style()->effectiveZoom()));
 }
 
 int Element::scrollWidth()
 {
     document().updateLayoutIgnorePendingStylesheets();
     if (RenderBox* rend = renderBox())
         return adjustForAbsoluteZoom(rend->scrollWidth(), rend);
     return 0;
 }
 
@@ skipping 2736 matching lines @@
     // Before doing so, we need to resolve issues in HTMLSelectElement::recalcListItems
     // and RenderMenuList::setText. See also https://bugs.webkit.org/show_bug.cgi?id=88405
     if (hasTagName(optionTag) || hasTagName(optgroupTag))
         return false;
     if (FullscreenElementStack::isActiveFullScreenElement(this))
         return false;
     return true;
 }
 
 } // namespace WebCore