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

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index f458c9f1012d87accf86ba99bc0cb4f3f5391235..c4e9b2c11014cd9ca5b0c73aaeefb9d1e1ca3c8c 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -301,8 +301,13 @@ void RenderLayer::updateLayerPositionRecursive(UpdateLayerPositionsFlags flags)
     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()