Invalidate previous paint rect in RenderObject::paintInvalidationForWholeRenderer()

Source/core/rendering/RenderObject.cpp

Index: Source/core/rendering/RenderObject.cpp
diff --git a/Source/core/rendering/RenderObject.cpp b/Source/core/rendering/RenderObject.cpp
index 8dda7f577f8695331ed04bbf4992cbd1e1e8631e..8dea4667c5019ae56859f06aac0aa667c76827b9 100644
--- a/Source/core/rendering/RenderObject.cpp
+++ b/Source/core/rendering/RenderObject.cpp
@@ -1533,6 +1533,8 @@ void RenderObject::paintInvalidationForWholeRenderer() const
     const RenderLayerModelObject* paintInvalidationContainer = containerForPaintInvalidation();
     LayoutRect paintInvalidationRect = boundsRectForPaintInvalidation(paintInvalidationContainer);
     invalidatePaintUsingContainer(paintInvalidationContainer, paintInvalidationRect, InvalidationPaint);
+    if (paintInvalidationRect != previousPaintInvalidationRect())
+        invalidatePaintUsingContainer(paintInvalidationContainer, previousPaintInvalidationRect(), InvalidationPaint);

[Julien - ping for review, 2014/07/15 00:58:31]

I think we should only invalidate the previousPaintInvalidation here actually.
The other invalidation above will invalidate at position we don't care about
(e.g. intermediate forced layout + style recalc between frames).

The reason is simple: all our invalidations should be based on the previous
stored rectangles (and positions), if we don't have any that means we didn't
push a frame so we don't care about invalidating.

[Xianzhu, 2014/07/15 01:16:24]

I tried that but layout test results showed under-paints. Most of such tests are
about transformations (perhaps in squashed layers), such as
fast/repaint/fixed-scale.html. Only the rects before change of transformations
were invalidated. It seems that code path is parallel with the normal RAL path
and expects this method to invalidate the current paint rect. Will look into the
callers in such cases, but I wonder if there are also other callers expecting
the same.

 }
 
 LayoutRect RenderObject::boundsRectForPaintInvalidation(const RenderLayerModelObject* paintInvalidationContainer) const