DocsUI: Update the drag shadow to meet UI spec.

BUG=27608249

Change-Id: If10f842be4507c5f04e2e91dadcae842610388f2
diff --git a/res/values/dimens.xml b/res/values/dimens.xml
index 5af7da3..e682994 100644
--- a/res/values/dimens.xml
+++ b/res/values/dimens.xml
@@ -38,4 +38,8 @@
     <dimen name="drag_shadow_size">120dp</dimen>
     <dimen name="grid_item_elevation">2dp</dimen>
     <dimen name="max_drawer_width">280dp</dimen>
+
+    <dimen name="drag_shadow_width">160dp</dimen>
+    <dimen name="drag_shadow_height">48dp</dimen>
+
 </resources>