Fix incorrect use of coords conversion for sticky elements

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index 3f7a58cdc7346e28159fd34c773fd4ea38c416e9..540edb7ca137c11d4ae8dc3bdf9831b81c603d02 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -316,8 +316,16 @@ void CompositedLayerMapping::UpdateStickyConstraints(
     // The enclosing layers offset returned from |convertToLayerCoords| must be
     // adjusted for both scroll and ancestor sticky elements.
     LayoutPoint enclosing_layer_offset;
-    compositing_container->ConvertToLayerCoords(ancestor_overflow_layer,
-                                                enclosing_layer_offset);
+    // The offset from the compositing_container to the ancestor_overflow_layer
+    // when we have a scroll parent is computed by the source_to_parent vector
+    // on the transform node.
+    // TODO(yigu): Eventually we want to remove the dependancy of
+    // source_to_parent from StickyPositionOffset in property_tree.cc.
+    if (!ScrollParent()) {
+      compositing_container->ConvertToLayerCoords(ancestor_overflow_layer,
+                                                  enclosing_layer_offset);
+    }
+
     DCHECK(!ScrollParent() || ScrollParent() == ancestor_overflow_layer);
     if (!ScrollParent() && compositing_container != ancestor_overflow_layer) {
       enclosing_layer_offset += LayoutSize(