[Android] Rework multidex and enable multidex for unit_tests_apk.

testing/test.gni

 # 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.
 
 # ==============================================================================
 # TEST SETUP
 # ==============================================================================
 
 # Define a test as an executable (or apk on Android) with the "testonly" flag
 # set.
@@ skipping 48 matching lines @@
           invoker.use_default_launcher) {
         deps += [ "//testing/android/native_test:native_test_native_code" ]
       }
     }
 
     unittest_apk(apk_name) {
       forward_variables_from(invoker,
                              [
                                "android_manifest",
                                "deps",
+                               "enable_multidex",
                                "use_default_launcher",
                                "write_asset_list",
                              ])
       unittests_dep = ":$library_name"
       apk_name = main_target_name
       if (defined(invoker.output_name)) {
         apk_name = invoker.output_name
         unittests_binary = "lib${apk_name}.so"
       }
       deps += [ ":$library_name" ]
@@ skipping 109 matching lines @@
         # All shared libraries must have the sanitizer deps to properly link in
         # asan mode (this target will be empty in other cases).
         "//build/config/sanitizers:deps",
 
         # Give tests the default manifest on Windows (a no-op elsewhere).
         "//build/win:default_exe_manifest",
       ]
     }
   }
 }