Refactor PanelLayoutManager to use aura::LayoutManager

ash/common/wm/wm_snap_to_pixel_layout_manager.cc

Index: ash/common/wm/wm_snap_to_pixel_layout_manager.cc
diff --git a/ash/common/wm/wm_snap_to_pixel_layout_manager.cc b/ash/common/wm/wm_snap_to_pixel_layout_manager.cc
index 79afc8959f080494fe688109b5c6bc053c834e07..7a604f11addf80e158e5f05fa84e89ba40f4d31e 100644
--- a/ash/common/wm/wm_snap_to_pixel_layout_manager.cc
+++ b/ash/common/wm/wm_snap_to_pixel_layout_manager.cc
@@ -24,7 +24,7 @@ void WmSnapToPixelLayoutManager::InstallOnContainers(WmWindow* window) {
         child->GetShellWindowId() > kShellWindowId_Max)  // not a container
       continue;
     if (child->aura_window()->GetProperty(kSnapChildrenToPixelBoundary)) {
-      if (!child->GetLayoutManager())
+      if (!child->GetLayoutManager() && !child->aura_window()->layout_manager())
         child->SetLayoutManager(base::MakeUnique<WmSnapToPixelLayoutManager>());
     } else {
       InstallOnContainers(child);