Fix Snackbar theme on sw600dp

Missed this layout in I9c91437a33eee99326f2bbfe9719667f598e005a

BUG: 30154587
Change-Id: I630dbe7a6b0d2065625906eaa0d40924f31f206f
diff --git a/design/res/layout-sw600dp/design_layout_snackbar.xml b/design/res/layout-sw600dp/design_layout_snackbar.xml
index b68395a..28835e5 100644
--- a/design/res/layout-sw600dp/design_layout_snackbar.xml
+++ b/design/res/layout-sw600dp/design_layout_snackbar.xml
@@ -20,4 +20,5 @@
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_gravity="bottom|center_horizontal"
+      android:theme="@style/ThemeOverlay.AppCompat.Dark"
       style="@style/Widget.Design.Snackbar" />
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