[S.P.] Invalidate the document element for view background when needed

Source/core/layout/LayoutObject.h

Index: Source/core/layout/LayoutObject.h
diff --git a/Source/core/layout/LayoutObject.h b/Source/core/layout/LayoutObject.h
index e1e005e128e46c62f23b0e0cad87b38cdbe05910..2e4d5cff9556ff8b768aa19caa76affd5c1cf663 100644
--- a/Source/core/layout/LayoutObject.h
+++ b/Source/core/layout/LayoutObject.h
@@ -256,11 +256,18 @@ public:
 #endif
 
     // FIXME: This could be used when changing the size of a renderer without children to skip some invalidations.
-    bool rendererHasNoBoxEffect() const
+    // FIXME: This is incorrect for document element. Remove this when we enable slimming paint.
+    bool rendererHasNoBoxEffectObsolete() const
     {
         return !style()->hasVisualOverflowingEffect() && !style()->hasBorder() && !style()->hasBackground();
     }

[Xianzhu, 2015/03/18 22:44:19]

Because the current code works well, I don't want to bother change it (which
will cause many layout test expectation changes). I'd like to keep the above old
code and remove it when we remove all the old code.

 
+    // Correct version of !rendererHasNoBoxEffectObsolete().
+    bool hasBoxEffect() const
+    {
+        return hasBoxDecorationBackground() || style()->hasVisualOverflowingEffect();

[Xianzhu, 2015/03/18 22:44:19]

hasBoxDecorationBackground() correctly considers the background of document
element.

+    }
+
     // Obtains the nearest enclosing block (including this block) that contributes a first-line style to our inline
     // children.
     virtual LayoutBlock* firstLineBlock() const;