Avoid clearing pointers on layers still in the mapping's vector of layers.
When adjusting layers, a particular layer may be added to a grouped
mapping at a location earlier than where it already appears in the
layer vector. When we then clear the unused entries in the list, we
remove the layer and null its group mapping, despite it still being
present earlier in the vector.
R=vollick
BUG=507988
Review URL: https://codereview.chromium.org/1227763002
git-svn-id: svn://svn.chromium.org/blink/trunk@198534 bbb929c8-8fbe-4397-9dbb-9b2b20218538
1 file changed
