Properly repaint RenderLayer's descendants when it moves

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 b3199f8a10a57700ffeb7a1761da4f42cb5ab1bc..531ad74e09af8161a956fb884e178b89ee51883f 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -257,9 +257,18 @@ void RenderLayer::updateLayerPositionsAfterLayout(const RenderLayer* rootLayer,
     updateLayerPositionRecursive(flags);
 }
 
+void RenderLayer::markDescendantLayersMayNeedPaintInvalidation()
+{
+    for (RenderLayer* childLayer = firstChild(); childLayer; childLayer = childLayer->nextSibling()) {

[esprehn, 2014/06/24 20:37:07]

We should take a different approach than this and mark a "Forced" update type on
this layer, and then during the walk the Force should make us traverse down the
subtree. What you've added here is going to walk down the subtree over and over
again.

+        childLayer->renderer()->setMayNeedPaintInvalidation(true);
+        childLayer->markDescendantLayersMayNeedPaintInvalidation();
+    }
+}
+
 void RenderLayer::updateLayerPositionRecursive(UpdateLayerPositionsFlags flags)
 {
-    updateLayerPosition();
+    if (updateLayerPosition())
+        markDescendantLayersMayNeedPaintInvalidation();

[esprehn, 2014/06/24 20:37:07]

Doesn't this make us traverse down the same subtree repeatedly?

 
     // Clear our cached clip rect information.
     m_clipper.clearClipRects();