Update alertDialogTheme to use proper colorAccent.

The settings dialogs were all using the default colorAccent.
Now it uses the app's version.

BUG: 28760785

Change-Id: Ic9bf90745db7d2ef5b1fd047474bab5c6bbdab23
diff --git a/res/values/themes.xml b/res/values/themes.xml
index 011957b..511e462 100644
--- a/res/values/themes.xml
+++ b/res/values/themes.xml
@@ -244,6 +244,7 @@
     </style>
 
     <style name="Theme.AlertDialog" parent="@*android:style/Theme.Material.Settings.Dialog.Alert">
+        <item name="android:colorAccent">@color/accent_color</item>
         <item name="android:windowSoftInputMode">adjustResize</item>
 
         <!-- Redefine the ActionBar style for contentInsetStart -->