[sms] Make sms dialog background color use sheet_bg_color

This CL changes sms dialog background color to use sheet_bg_color so
that when Chrome changes to different theme, the dialog background is
also changed. This is to fix the text on the dialog not visible when
Chrome changes to dark theme.

I uploaded some dialog screenshots when using default theme and dark
theme on the issue page.

Bug: 991392
Change-Id: Ib685689e7f150a09243edf9d02b61b166ea54276
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1749764Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: Jun Cai <juncai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686412}

chrome/android/java/res/drawable/sms_receiver_dialog_background.xml

@@ -4,6 +4,6 @@
      found in the LICENSE file. -->
 
 <shape xmlns:android="http://schemas.android.com/apk/res/android">
-    <solid android:color="@color/default_bg_color_light"/>
+    <solid android:color="@color/sheet_bg_color"/>
     <corners android:radius="10dp"/>
 </shape>