Changes threshold frequency for investigation (based on video in the bug)

ash/common/shelf/wm_shelf.h

Index: ash/common/shelf/wm_shelf.h
diff --git a/ash/common/shelf/wm_shelf.h b/ash/common/shelf/wm_shelf.h
index 4b96c01cba014617a17e84cd398f4638dbde6194..0e97159bc4a7ab244d6365123009c6c3a684bc82 100644
--- a/ash/common/shelf/wm_shelf.h
+++ b/ash/common/shelf/wm_shelf.h
@@ -24,6 +24,7 @@ class GestureEvent;
 namespace ash {
 
 class ShelfLayoutManager;
+class ShelfLayoutManagerTest;
 class ShelfLockingManager;
 class ShelfView;
 class ShelfWidget;
@@ -146,6 +147,8 @@ class ASH_EXPORT WmShelf : public ShelfLayoutManagerObserver {
                            BackgroundAnimatorChangeType change_type) override;
 
  private:
+  friend class ShelfLayoutManagerTest;
+
   // Layout manager for the shelf container window. Instances are constructed by
   // ShelfWidget and lifetimes are managed by the container windows themselves.
   ShelfLayoutManager* shelf_layout_manager_ = nullptr;