Get rid of slow repaint objects and main thread scrolling reasons.

sky/engine/core/rendering/RenderObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1820 matching lines @@
         // Clearing these bits is required to avoid leaving stale renderers.
         // FIXME: We shouldn't need that hack if our logic was totally correct.
         if (diff.needsLayout()) {
             setFloating(false);
             clearPositionedState();
         }
     } else {
         s_affectsParentBlock = false;
     }
 
-    if (view()->frameView()) {
-        bool shouldBlitOnFixedBackgroundImage = false;
-        if (RuntimeEnabledFeatures::fastMobileScrollingEnabled()) {
-            // On low-powered/mobile devices, preventing blitting on a scroll can cause noticeable delays
-            // when scrolling a page with a fixed background image. As an optimization, assuming there are
-            // no fixed positoned elements on the page, we can acclerate scrolling (via blitting) if we
-            // ignore the CSS property "background-attachment: fixed".
-            shouldBlitOnFixedBackgroundImage = true;
-        }
-        bool newStyleSlowScroll = !shouldBlitOnFixedBackgroundImage && newStyle.hasFixedBackgroundImage();
-        bool oldStyleSlowScroll = m_style && !shouldBlitOnFixedBackgroundImage && m_style->hasFixedBackgroundImage();
-
-        bool drawsRootBackground = isDocumentElement();
-        if (drawsRootBackground && !shouldBlitOnFixedBackgroundImage) {
-            if (view()->compositor()->supportsFixedRootBackgroundCompositing()) {
-                if (newStyleSlowScroll && newStyle.hasEntirelyFixedBackground())
-                    newStyleSlowScroll = false;
-
-                if (oldStyleSlowScroll && m_style->hasEntirelyFixedBackground())
-                    oldStyleSlowScroll = false;
-            }
-        }
-
-        if (oldStyleSlowScroll != newStyleSlowScroll) {
-            if (oldStyleSlowScroll)
-                view()->frameView()->removeSlowRepaintObject();
-            if (newStyleSlowScroll)
-                view()->frameView()->addSlowRepaintObject();
-        }
-    }
-
     // Elements with non-auto touch-action will send a SetTouchAction message
     // on touchstart in EventHandler::handleTouchEvent, and so effectively have
     // a touchstart handler that must be reported.
     //
     // Since a CSS property cannot be applied directly to a text node, a
     // handler will have already been added for its parent so ignore it.
     TouchAction oldTouchAction = m_style ? m_style->touchAction() : TouchActionAuto;
     if (node() && !node()->isTextNode() && (oldTouchAction == TouchActionAuto) != (newStyle.touchAction() == TouchActionAuto)) {
         EventHandlerRegistry& registry = document().frameHost()->eventHandlerRegistry();
         if (newStyle.touchAction() != TouchActionAuto)
@@ skipping 1006 matching lines @@
 {
     if (object1) {
         const blink::RenderObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showRenderTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif