Revert "Ignore should-scroll-on-main-thread if main frame is not scrollable"

Source/core/page/scrolling/ScrollingCoordinator.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 72 matching lines @@
 
 PassRefPtr<ScrollingCoordinator> ScrollingCoordinator::create(Page* page)
 {
     return adoptRef(new ScrollingCoordinator(page));
 }
 
 ScrollingCoordinator::ScrollingCoordinator(Page* page)
     : m_page(page)
     , m_scrollGestureRegionIsDirty(false)
     , m_touchEventTargetRectsAreDirty(false)
-    , m_wasFrameScrollable(false)
-    , m_lastMainThreadScrollingReasons(0)
 {
 }
 
 ScrollingCoordinator::~ScrollingCoordinator()
 {
     ASSERT(!m_page);
     for (ScrollbarMap::iterator it = m_horizontalScrollbars.begin(); it != m_horizontalScrollbars.end(); ++it)
         GraphicsLayer::unregisterContentsLayer(it->value->layer());
     for (ScrollbarMap::iterator it = m_verticalScrollbars.begin(); it != m_verticalScrollbars.end(); ++it)
         GraphicsLayer::unregisterContentsLayer(it->value->layer());
@@ skipping 41 matching lines @@
         Region shouldHandleScrollGestureOnMainThreadRegion = computeShouldHandleScrollGestureOnMainThreadRegion(m_page->mainFrame(), IntPoint());
         setShouldHandleScrollGestureOnMainThreadRegion(shouldHandleScrollGestureOnMainThreadRegion);
         m_scrollGestureRegionIsDirty = false;
     }
 
     if (m_touchEventTargetRectsAreDirty) {
         updateTouchEventTargetRectsIfNeeded();
         m_touchEventTargetRectsAreDirty = false;
     }
 
-    FrameView* frameView = m_page->mainFrame()->view();
-    bool frameIsScrollable = frameView && frameView->isScrollable();
-    if (m_wasFrameScrollable != frameIsScrollable)
-        updateShouldUpdateScrollLayerPositionOnMainThread();
-    m_wasFrameScrollable = frameIsScrollable;
-
     const FrameTree& tree = m_page->mainFrame()->tree();
     for (const Frame* child = tree.firstChild(); child; child = child->tree().nextSibling()) {
         if (WebLayer* scrollLayer = scrollingWebLayerForScrollableArea(child->view()))
             scrollLayer->setBounds(child->view()->contentsSize());
     }
 }
 
 void ScrollingCoordinator::setLayerIsContainerForFixedPositionLayers(GraphicsLayer* layer, bool enable)
 {
     if (WebLayer* scrollableLayer = scrollingWebLayerForGraphicsLayer(layer))
@@ skipping 422 matching lines @@
 }
 
 void ScrollingCoordinator::recomputeWheelEventHandlerCountForFrameView(FrameView* frameView)
 {
     UNUSED_PARAM(frameView);
     setWheelEventHandlerCount(computeCurrentWheelEventHandlerCount());
 }
 
 void ScrollingCoordinator::setShouldUpdateScrollLayerPositionOnMainThread(MainThreadScrollingReasons reasons)
 {
-    if (WebLayer* scrollLayer = scrollingWebLayerForScrollableArea(m_page->mainFrame()->view())) {
-        m_lastMainThreadScrollingReasons = reasons;
+    if (WebLayer* scrollLayer = scrollingWebLayerForScrollableArea(m_page->mainFrame()->view()))
         scrollLayer->setShouldScrollOnMainThread(reasons);
-    }
 }
 
 void ScrollingCoordinator::pageDestroyed()
 {
     ASSERT(m_page);
     m_page = 0;
 }
 
 bool ScrollingCoordinator::coordinatesScrollingForFrameView(FrameView* frameView) const
 {
@@ skipping 244 matching lines @@
         // Composited layers that actually paint into their enclosing ancestor
         // must also force main thread scrolling.
         if (layer->compositingState() == HasOwnBackingButPaintsIntoAncestor)
             return true;
     }
     return false;
 }
 
 MainThreadScrollingReasons ScrollingCoordinator::mainThreadScrollingReasons() const
 {
-    // The main thread scrolling reasons are applicable to scrolls of the main
-    // frame. If it does not exist or if it is not scrollable, there is no
-    // reason to force main thread scrolling.
     FrameView* frameView = m_page->mainFrame()->view();
-    if (!frameView || !frameView->isScrollable())
+    if (!frameView)
         return static_cast<MainThreadScrollingReasons>(0);
 
     MainThreadScrollingReasons mainThreadScrollingReasons = (MainThreadScrollingReasons)0;
 
     if (frameView->hasSlowRepaintObjects())
         mainThreadScrollingReasons |= HasSlowRepaintObjects;
     if (hasVisibleSlowRepaintViewportConstrainedObjects(frameView))
         mainThreadScrollingReasons |= HasNonLayerViewportConstrainedObjects;
 
     return mainThreadScrollingReasons;
@@ skipping 15 matching lines @@
     if (reasons & ScrollingCoordinator::HasNonLayerViewportConstrainedObjects)
         stringBuilder.append("Has non-layer viewport-constrained objects, ");
 
     if (stringBuilder.length())
         stringBuilder.resize(stringBuilder.length() - 2);
     return stringBuilder.toString();
 }
 
 String ScrollingCoordinator::mainThreadScrollingReasonsAsText() const
 {
-    return mainThreadScrollingReasonsAsText(m_lastMainThreadScrollingReasons);
+    return mainThreadScrollingReasonsAsText(mainThreadScrollingReasons());
 }
 
 } // namespace WebCore