pt 1 in reviving the android build (copied from pm 28a1, wish me luck)

mobile/android/base/resources/drawable/widget_button_middle.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<selector xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <item android:state_pressed="true"
+           android:drawable="@drawable/widget_button_middle_pressed"/>
+
+    <item android:drawable="@android:color/transparent"/>
+
+</selector>