[New Multicolumn] Correct paint rectangle calculation for compositing.

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1473 matching lines @@
     ClipRect outlineRectInFlowThread;
     clipper().calculateRects(paginationClipRectsContext, PaintInfo::infiniteRect(), layerBoundsInFlowThread, backgroundRectInFlowThread, foregroundRectInFlowThread,
         outlineRectInFlowThread, &offsetWithinPaginatedLayer);
 
     // Take our bounding box within the flow thread and clip it.
     LayoutRect layerBoundingBoxInFlowThread = layerBoundingBox ? *layerBoundingBox : physicalBoundingBox(enclosingPaginationLayer(), &offsetWithinPaginatedLayer);
     layerBoundingBoxInFlowThread.intersect(backgroundRectInFlowThread.rect());
 
     // Shift the dirty rect into flow thread coordinates.
     LayoutPoint offsetOfPaginationLayerFromRoot;
-    enclosingPaginationLayer()->convertToLayerCoords(rootLayer, offsetOfPaginationLayerFromRoot);
+    if (rootLayer != enclosingPaginationLayer() && rootLayer->enclosingPaginationLayer() == enclosingPaginationLayer()) {
+        // The root layer is inside our pagination layer.
+        // FIXME: more work needed if there are nested pagination layers.
+        rootLayer->convertToLayerCoords(enclosingPaginationLayer(), offsetOfPaginationLayerFromRoot);
+        offsetOfPaginationLayerFromRoot = -offsetOfPaginationLayerFromRoot;
+    } else {
+        enclosingPaginationLayer()->convertToLayerCoords(rootLayer, offsetOfPaginationLayerFromRoot);
+    }
     LayoutRect dirtyRectInFlowThread(dirtyRect);
     dirtyRectInFlowThread.moveBy(-offsetOfPaginationLayerFromRoot);
 
     // Tell the flow thread to collect the fragments. We pass enough information to create a minimal number of fragments based off the pages/columns
     // that intersect the actual dirtyRect as well as the pages/columns that intersect our layer's bounding box.
     RenderFlowThread* enclosingFlowThread = toRenderFlowThread(enclosingPaginationLayer()->renderer());
     enclosingFlowThread->collectLayerFragments(fragments, layerBoundingBoxInFlowThread, dirtyRectInFlowThread);
 
     if (fragments.isEmpty())
         return;
@@ skipping 1346 matching lines @@
     }
 }
 
 void showLayerTree(const blink::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif