Update tablet dialog background for FRE

Bug: 900755
Change-Id: Ie4bc5f815fe698594de99fde68517ccb0bd6a105
Reviewed-on: https://chromium-review.googlesource.com/c/1340608
Commit-Queue: Becky Zhou <huayinz@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609361}

chrome/android/java/res/drawable-sw600dp/bg_white_dialog.xml

@@ -3,10 +3,5 @@
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file. -->
 
-<shape xmlns:android="http://schemas.android.com/apk/res/android"
-    android:shape="rectangle">
-    <corners
-        android:radius="2dp" />
-    <solid
-        android:color="@android:color/white" />
-</shape>
\ No newline at end of file
+<nine-patch xmlns:android="http://schemas.android.com/apk/res/android"
+    android:src="@drawable/popup_bg" />