Move ChromiumMultiDex to BuildConfig.

base/android/java/templates/ChromiumMultiDex.template

-// Copyright 2015 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.
-
-package org.chromium.base.multidex;
-
-/**
- *  Multidex configuration. Generated on a per-target basis.
- */
-class ChromiumMultiDex {
-
-    /** Whether multidex is enabled for this target.
-     *
-     *  This has to be a function instead of a static final boolean s.t. the initial false value
-     *  doesn't get optimized into {@link ChromiumMultiDexInstaller} at base_java compile time.
-     */
-    static boolean isMultidexEnabled() {
-#if defined(ENABLE_MULTIDEX)
-        return true;
-#else
-        return false;
-#endif
-    }
-
-}