Repaint squashing content in cases where the entire frame is repainting.

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 283 matching lines @@
         updatePagination();
         flags |= UpdatePagination;
     }
 
     if (renderer()->hasColumns())
         flags |= UpdatePagination;
 
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->updateLayerPositionRecursive(flags);
 
-    if ((flags & NeedsFullRepaintInBacking) && hasCompositedLayerMapping() && !compositedLayerMapping()->paintsIntoCompositedAncestor())
+    // FIXME: why isn't FrameView just calling RenderLayerCompositor::repaintCompositedLayers? Does it really impact
+    // performance?

[abarth-chromium, 2014/06/13 22:14:01]

Because this code is crazy.

+    if ((flags & NeedsFullRepaintInBacking) && hasCompositedLayerMapping() && !compositedLayerMapping()->paintsIntoCompositedAncestor()) {
         compositedLayerMapping()->setContentsNeedDisplay();
+        // This code is called when the FrameView wants to repaint the entire frame. This includes squashing content.
+        compositedLayerMapping()->setSquashingContentsNeedDisplay();

[abarth-chromium, 2014/06/13 22:14:01]

Are there any callers of setContentsNeedDisplay() that don't want to call
setSquashingContentsNeedDisplay()?  Perhaps setContentsNeedDisplay() should do
the work of setSquashingContentsNeedDisplay() as well.

[chrishtr, 2014/06/13 22:48:33]

Yes, there is one, which is why I didn't do it that way. In particular,
CompositedLayerMapping::updateFilters(). I don't want to
over-invalidate.

+    }
 }
 
 void RenderLayer::setAncestorChainHasSelfPaintingLayerDescendant()
 {
     for (RenderLayer* layer = this; layer; layer = layer->parent()) {
         if (!layer->m_hasSelfPaintingLayerDescendantDirty && layer->hasSelfPaintingLayerDescendant())
             break;
 
         layer->m_hasSelfPaintingLayerDescendantDirty = false;
         layer->m_hasSelfPaintingLayerDescendant = true;
@@ skipping 3514 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif