Unable to scroll in Chrome system URLs(history,settings,extension) pages

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 1236 matching lines @@
 void FrameView::scrollContentsIfNeeded()
 {
     bool didScroll = !pendingScrollDelta().isZero();
     ScrollView::scrollContentsIfNeeded();
     if (didScroll)
         updateFixedElementPaintInvalidationRectsAfterScroll();
 }
 
 bool FrameView::scrollContentsFastPath(const IntSize& scrollDelta, const IntRect& rectToScroll)
 {
+    if (!contentsInCompositedLayer())
+        return false;
+
     if (!m_viewportConstrainedObjects || m_viewportConstrainedObjects->isEmpty()) {
         hostWindow()->scroll();
         return true;
     }
 
-    const bool isCompositedContentLayer = contentsInCompositedLayer();
-
     // Get the rects of the fixed objects visible in the rectToScroll
     Region regionToUpdate;
     ViewportConstrainedObjectSet::const_iterator end = m_viewportConstrainedObjects->end();
     for (ViewportConstrainedObjectSet::const_iterator it = m_viewportConstrainedObjects->begin(); it != end; ++it) {
         RenderObject* renderer = *it;
         // m_viewportConstrainedObjects should not contain non-viewport constrained objects.
         ASSERT(renderer->style()->hasViewportConstrainedPosition());
 
         // Fixed items should always have layers.
         ASSERT(renderer->hasLayer());
         RenderLayer* layer = toRenderBoxModelObject(renderer)->layer();
 
         // Layers that paint into their ancestor or into a grouped backing will still need
         // to apply a paint invalidation. If the layer paints into its own backing, then
         // it does not need paint invalidation just to scroll.
         if (layer->compositingState() == PaintsIntoOwnBacking)
             continue;
 
         if (layer->hasAncestorWithFilterOutsets()) {
             // If the fixed layer has a blur/drop-shadow filter applied on at least one of its parents, we cannot
             // scroll using the fast path, otherwise the outsets of the filter will be moved around the page.
             return false;
         }
 
         IntRect updateRect = pixelSnappedIntRect(layer->repainter().repaintRectIncludingNonCompositingDescendants());
 
         const RenderLayerModelObject* repaintContainer = layer->renderer()->containerForPaintInvalidation();
         if (repaintContainer && !repaintContainer->isRenderView()) {
-            // If the fixed-position layer is contained by a composited layer that is not its containing block,
-            // then we have to invalidate that enclosing layer, not the RenderView.
-            // FIXME: Why do we need to issue this invalidation? Won't the fixed position element just scroll
-            //        with the enclosing layer.
+            // Invalidate the old and new locations of fixed position elements that are not drawn into the RenderView.
             updateRect.moveBy(scrollPosition());
             IntRect previousRect = updateRect;
             previousRect.move(scrollDelta);
+            // FIXME: Rather than uniting the rects, we should just issue both invalidations.
             updateRect.unite(previousRect);
             layer->renderer()->invalidatePaintUsingContainer(repaintContainer, updateRect, InvalidationScroll);
         } else {
             // Coalesce the paint invalidations that will be issued to the renderView.
             updateRect = contentsToRootView(updateRect);
-            if (!isCompositedContentLayer && clipsPaintInvalidations())
-                updateRect.intersect(rectToScroll);
             if (!updateRect.isEmpty())
                 regionToUpdate.unite(updateRect);
         }
     }
 
-    // 1) scroll
     hostWindow()->scroll();
 
-    // 2) update the area of fixed objects that has been invalidated
+    // Invalidate the old and new locations of fixed position elements that are drawn into the RenderView.
     Vector<IntRect> subRectsToUpdate = regionToUpdate.rects();
     size_t viewportConstrainedObjectsCount = subRectsToUpdate.size();
     for (size_t i = 0; i < viewportConstrainedObjectsCount; ++i) {
         IntRect updateRect = subRectsToUpdate[i];
         IntRect scrolledRect = updateRect;
         scrolledRect.move(-scrollDelta);
         updateRect.unite(scrolledRect);
-        if (isCompositedContentLayer) {
-            updateRect = rootViewToContents(updateRect);
-            ASSERT(renderView());
-            renderView()->layer()->repainter().setBackingNeedsRepaintInRect(updateRect);
-            continue;
-        }
-        if (clipsPaintInvalidations())
-            updateRect.intersect(rectToScroll);
-        hostWindow()->invalidateContentsAndRootView(updateRect);
+        // FIXME: We should be able to issue these invalidations separately and before we actually scroll.
+        renderView()->layer()->repainter().setBackingNeedsRepaintInRect(rootViewToContents(updateRect));
     }
 
     return true;
 }
 
 void FrameView::scrollContentsSlowPath(const IntRect& updateRect)
 {
     if (contentsInCompositedLayer()) {
         IntRect updateRect = visibleContentRect();
         ASSERT(renderView());
@@ skipping 1803 matching lines @@
 void FrameView::willRemoveScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
 {
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache()) {
         cache->remove(scrollbar);
         cache->handleScrollbarUpdate(this);
     }
 }
 
 } // namespace blink