Get rid of one-off code in ScrollingCoordinator to handle graphics layer offsets.

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 401 matching lines @@
             continue;
         const RenderLayer* containingLayer = ownerRenderer->enclosingLayer();
         LayerFrameMap::iterator iter = map->find(containingLayer);
         if (iter == map->end())
             map->add(containingLayer, Vector<const LocalFrame*>()).storedValue->value.append(toLocalFrame(child));
         else
             iter->value.append(toLocalFrame(child));
     }
 }
 
-// Return the enclosingCompositedLayerForRepaint for the given RenderLayer
+// Return the enclosingCompositedLayerForPaintInvalidation for the given RenderLayer
 // including crossing frame boundaries.
 static const RenderLayer* enclosingCompositedLayer(const RenderLayer* layer)
 {
     RenderLayer* compositedLayer = 0;
     while (!compositedLayer) {
         compositedLayer = layer->enclosingCompositingLayerForPaintInvalidation();
         if (!compositedLayer) {
             RenderObject* owner = layer->renderer()->frame()->ownerRenderer();
             if (!owner)
                 break;
@@ skipping 17 matching lines @@
     // Project any rects for the current layer
     LayerHitTestRects::const_iterator layerIter = layerRects.find(curLayer);
     if (layerIter != layerRects.end()) {
         // Find the enclosing composited layer when it's in another document (for non-composited iframes).
         const RenderLayer* compositedLayer = enclosingCompositedLayer(layerIter->key);
         if (!compositedLayer)
             return;
 
         // Find the appropriate GraphicsLayer for the composited RenderLayer.
         GraphicsLayer* graphicsLayer;
-        LayoutSize extraOffset;
         if (compositedLayer->compositingState() == PaintsIntoGroupedBacking) {
             graphicsLayer = compositedLayer->groupedMapping()->squashingLayer();
-            extraOffset = -compositedLayer->offsetFromSquashingLayerOrigin();
         } else {
             ASSERT(compositedLayer->hasCompositedLayerMapping());
             CompositedLayerMappingPtr compositedLayerMapping = compositedLayer->compositedLayerMapping();
-            // The origin for the graphics layer does not have to be the same
-            // as the composited layer (e.g. when a child layer has negative
-            // offset and paints into this layer), so when projecting rects to
-            // graphics layer space they have to be offset by the origin for
-            // the composited layer.
-            extraOffset = compositedLayerMapping->contentOffsetInCompositingLayer();
-            // If the layer is using composited scrolling, then it's the contents that these
-            // rects apply to.
             graphicsLayer = compositedLayerMapping->scrollingContentsLayer();
             if (!graphicsLayer)
                 graphicsLayer = compositedLayerMapping->mainGraphicsLayer();
         }
 
         GraphicsLayerHitTestRects::iterator glIter = graphicsRects.find(graphicsLayer);
         Vector<LayoutRect>* glRects;
         if (glIter == graphicsRects.end())
             glRects = &graphicsRects.add(graphicsLayer, Vector<LayoutRect>()).storedValue->value;
         else
             glRects = &glIter->value;
+
         // Transform each rect to the co-ordinate space of the graphicsLayer.
         for (size_t i = 0; i < layerIter->value.size(); ++i) {
             LayoutRect rect = layerIter->value[i];
             if (compositedLayer != curLayer) {
                 FloatQuad compositorQuad = geometryMap.mapToContainer(rect, compositedLayer->renderer());
                 rect = LayoutRect(compositorQuad.boundingBox());
                 // If the enclosing composited layer itself is scrolled, we have to undo the subtraction
                 // of its scroll offset since we want the offset relative to the scrolling content, not
                 // the element itself.
                 if (compositedLayer->renderer()->hasOverflowClip())
                     rect.move(compositedLayer->renderBox()->scrolledContentOffset());
             }
-            rect.move(extraOffset);
+            RenderLayer::mapRectToPaintBackingCoordinates(compositedLayer->renderer(), rect);
             glRects->append(rect);
         }
     }
 
     // Walk child layers of interest
     for (const RenderLayer* childLayer = curLayer->firstChild(); childLayer; childLayer = childLayer->nextSibling()) {
         if (layersWithRects.contains(childLayer)) {
             geometryMap.pushMappingsToAncestor(childLayer, curLayer);
             projectRectsToGraphicsLayerSpaceRecursive(childLayer, layerRects, graphicsRects, geometryMap, layersWithRects, layerChildFrameMap);
             geometryMap.popMappingsToAncestor(curLayer);
@@ skipping 491 matching lines @@
     bool frameIsScrollable = frameView && frameView->isScrollable();
     if (frameIsScrollable != m_wasFrameScrollable)
         return true;
 
     if (WebLayer* scrollLayer = frameView ? toWebLayer(frameView->layerForScrolling()) : 0)
         return blink::WebSize(frameView->contentsSize()) != scrollLayer->bounds();
     return false;
 }
 
 } // namespace WebCore