Set geometry dirty bits on composited layer mappings when updating squashed layers.

Source/core/rendering/compositing/CompositedLayerMapping.cpp

Index: Source/core/rendering/compositing/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.cpp b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
index 1997accd403e335080362befcb932f53bcb2f9ff..d5d89fb11d3af8df3030fb8e20a7f117c1311a6c 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -2064,6 +2064,7 @@ bool CompositedLayerMapping::updateSquashingLayerAssignment(RenderLayer* layer,
         updatedAssignment = true;
     }
     layer->setGroupedMapping(this);
+    setNeedsGeometryUpdate();

[abarth-chromium, 2014/03/17 17:17:03]

Should we move this call inside setGroupedMapping?  Don't if the grouped mapping
was non-zero before, don't we need to dirty the old composited layer mapping
too?

[chrishtr, 2014/03/17 18:10:55]

Done.

     return updatedAssignment;
 }