Revert "Reworks the clipping logic" and follow-up.

Source/core/paint/DeprecatedPaintLayer.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 358 matching lines @@
 
     bool hadTransform = m_transform;
     if (hasTransform != hadTransform) {
         if (hasTransform)
             m_transform = adoptPtr(new TransformationMatrix);
         else
             m_transform.clear();
 
         // DeprecatedPaintLayers with transforms act as clip rects roots, so clear the cached clip rects here.
         m_clipper.clearClipRectsIncludingDescendants();
+    } else if (hasTransform) {
+        m_clipper.clearClipRectsIncludingDescendants(AbsoluteClipRects);
     }
 
     updateTransformationMatrix();
 
     if (had3DTransform != has3DTransform())
         dirty3DTransformedDescendantStatus();
 }
 
 static DeprecatedPaintLayer* enclosingLayerForContainingBlock(DeprecatedPaintLayer* layer)
 {
@@ skipping 1004 matching lines @@
         appendSingleFragmentIgnoringPagination(fragments, rootLayer, dirtyRect, clipRectsCacheSlot, inOverlayScrollbarSizeRelevancy, respectOverflowClip, offsetFromRoot, subPixelAccumulation);
         return;
     }
 
     // Compute our offset within the enclosing pagination layer.
     LayoutPoint offsetWithinPaginatedLayer;
     convertToLayerCoords(enclosingPaginationLayer(), offsetWithinPaginatedLayer);
 
     // Calculate clip rects relative to the enclosingPaginationLayer. The purpose of this call is to determine our bounds clipped to intermediate
     // layers between us and the pagination context. It's important to minimize the number of fragments we need to create and this helps with that.
-    // This code uses a non-standard root layer, which can populate our cache with unexpected values.
-    // Thus we bypass the clip rect cache by ignoring |clipRectsCacheSlot| and passing UncachedClipRects.
-    // TODO(chadarmstrong): If possible, this code should use the cache (one way would be by computing the root layer relative to |clipRectsCacheSlot|).
-    ClipRectsContext paginationClipRectsContext(enclosingPaginationLayer(), UncachedClipRects, inOverlayScrollbarSizeRelevancy);
+    ClipRectsContext paginationClipRectsContext(enclosingPaginationLayer(), clipRectsCacheSlot, inOverlayScrollbarSizeRelevancy);
     if (respectOverflowClip == IgnoreOverflowClip)
         paginationClipRectsContext.setIgnoreOverflowClip();
     LayoutRect layerBoundsInFlowThread;
     ClipRect backgroundRectInFlowThread;
     ClipRect foregroundRectInFlowThread;
     ClipRect outlineRectInFlowThread;
     clipper().calculateRects(paginationClipRectsContext, LayoutRect(LayoutRect::infiniteIntRect()), layerBoundsInFlowThread, backgroundRectInFlowThread, foregroundRectInFlowThread,
         outlineRectInFlowThread, &offsetWithinPaginatedLayer);
 
     // Take our bounding box within the flow thread and clip it.
@@ skipping 18 matching lines @@
     // that intersect the actual dirtyRect as well as the pages/columns that intersect our layer's bounding box.
     enclosingFlowThread->collectLayerFragments(fragments, layerBoundingBoxInFlowThread, dirtyRectInFlowThread);
 
     if (fragments.isEmpty())
         return;
 
     // Get the parent clip rects of the pagination layer, since we need to intersect with that when painting column contents.
     ClipRect ancestorClipRect = dirtyRect;
     if (const DeprecatedPaintLayer* paginationParentLayer = enclosingPaginationLayer()->parent()) {
         const DeprecatedPaintLayer* ancestorLayer = rootLayerIsInsidePaginationLayer ? paginationParentLayer : rootLayer;
-        // This code uses a non-standard root layer, which can populate our cache with unexpected values.
-        // Thus we bypass the clip rect cache by ignoring |clipRectsCacheSlot| and passing UncachedClipRects.
-        // TODO(chadarmstrong): If possible, this code should use the cache (one way would be by computing the root layer relative to |clipRectsCacheSlot|).
-        ClipRectsContext clipRectsContext(ancestorLayer, UncachedClipRects, inOverlayScrollbarSizeRelevancy);
+        ClipRectsContext clipRectsContext(ancestorLayer, clipRectsCacheSlot, inOverlayScrollbarSizeRelevancy);
         if (respectOverflowClip == IgnoreOverflowClip)
             clipRectsContext.setIgnoreOverflowClip();
         ancestorClipRect = enclosingPaginationLayer()->clipper().backgroundClipRect(clipRectsContext);
         if (rootLayerIsInsidePaginationLayer)
             ancestorClipRect.moveBy(-rootLayer->visualOffsetFromAncestor(ancestorLayer));
         ancestorClipRect.intersect(dirtyRect);
     }
 
     const LayoutSize subPixelAccumulationIfNeeded = offsetFromRoot ? subPixelAccumulation : LayoutSize();
     for (size_t i = 0; i < fragments.size(); ++i) {
@@ skipping 1285 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif