Open root list when hovering on the edge in drawer layout.

Bug: 28345294

Change-Id: Ia569003e21aea0641ccc1d2a5e042bdc93f32bb3
diff --git a/res/values/dimens.xml b/res/values/dimens.xml
index e682994..cad26e2 100644
--- a/res/values/dimens.xml
+++ b/res/values/dimens.xml
@@ -39,6 +39,8 @@
     <dimen name="grid_item_elevation">2dp</dimen>
     <dimen name="max_drawer_width">280dp</dimen>
 
+    <dimen name="drawer_edge_width">12dp</dimen>
+
     <dimen name="drag_shadow_width">160dp</dimen>
     <dimen name="drag_shadow_height">48dp</dimen>