[Android] Keep extracted secondary dex files when clearing data in tests. (RELAND)

build/android/main_dex_classes.flags

 # Copyright 2017 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Proguard flags for what should be kept in the main dex. Only used
 # during main dex list determination, not during actual proguarding.
 
 -keep @**.MainDex class * {
   *;
 }
 
 -keepclasseswithmembers class * {
   public static ** asInterface(android.os.IBinder);
 }
 
 # Required when code coverage is enabled.
 -keep class com.vladium.** {
-    *;
+  *;
 }
+
+# Used by tests for secondary dex extraction.
+-keep class android.support.v4.content.ContextCompat {
+  *;
+}