Removing a RenderLayer's CLM should trigger a repaint

Source/core/rendering/compositing/RenderLayerCompositor.cpp

Index: Source/core/rendering/compositing/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/compositing/RenderLayerCompositor.cpp b/Source/core/rendering/compositing/RenderLayerCompositor.cpp
index 81603f801f981f1f2d05c5322fefc8b5cb3b13c7..bea0a6d2e8e8b6340b7996aca6cc34f7f903c117 100644
--- a/Source/core/rendering/compositing/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/compositing/RenderLayerCompositor.cpp
@@ -480,8 +480,14 @@ bool RenderLayerCompositor::updateLayerIfViewportConstrained(RenderLayer* layer)
 // See crbug.com/383191 for a list of tests that fail if this method is removed.
 void RenderLayerCompositor::applyUpdateLayerCompositingStateChickenEggHacks(RenderLayer* layer, CompositingStateTransitionType compositedLayerUpdate)
 {
-    if (compositedLayerUpdate != NoCompositingStateChange)
-        allocateOrClearCompositedLayerMapping(layer, compositedLayerUpdate);
+    if (compositedLayerUpdate != NoCompositingStateChange) {
+        bool compositedLayerMappingChanged = allocateOrClearCompositedLayerMapping(layer, compositedLayerUpdate);
+        if (compositedLayerMappingChanged) {
+            if (layer->parent())

[chrishtr, 2014/06/13 15:45:38]

Please add a comment here about why the layer->parent() part is here, as well as
why parent() will
always be non-null in cases when the layer is attached. We had no idea why the
old conditional was there,
which is why I removed it.

[ajuma, 2014/06/13 18:03:50]

Done.

+                layer->repainter().computeRepaintRectsIncludingNonCompositingDescendants();

[ajuma, 2014/06/13 14:54:52]

I also needed to make this call conditional on having a parent (matching the
logic that used to exist in allocateOrClearCompositedLayerMapping for the case
of allocating a new mapping) -- the chicken-egg compositing update can happen
before a RenderObject is added to the render tree (see the logic in
RenderTreeBuilder::createRendererForElementIfNeeded, where the compositing
update happens during the call to setStyle, which happens before the
RenderObject is added to its parent), but trying to compute repaint rects
without a parent leads to a crash in
RenderTableCell::clippedOverflowRectForRepaint, since this assumes a non-null
parent.

+            repaintOnCompositingChange(layer);
+        }
+    }
 }
 
 void RenderLayerCompositor::updateLayerCompositingState(RenderLayer* layer, UpdateLayerCompositingStateOptions options)