Move scrim from DragLayer to LauncherRootView.

This change will make opening/closing animations a lot cleaner.

Change-Id: I7f8ae301a9a126023833e282d6654bebd09bb306
diff --git a/res/layout-sw720dp/launcher.xml b/res/layout-sw720dp/launcher.xml
index 7e6c659..fe2f108 100644
--- a/res/layout-sw720dp/launcher.xml
+++ b/res/layout-sw720dp/launcher.xml
@@ -21,6 +21,7 @@
     android:id="@+id/launcher"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
+    android:background="?attr/workspaceStatusBarScrim"
     android:fitsSystemWindows="true">
 
     <com.android.launcher3.dragndrop.DragLayer
@@ -28,7 +29,6 @@
         android:clipChildren="false"
         android:clipToPadding="false"
         android:importantForAccessibility="no"
-        android:background="?attr/workspaceStatusBarScrim"
         android:layout_width="match_parent"
         android:layout_height="match_parent">