[Android] Rework multidex and enable multidex for unit_tests_apk.

build/config/android/rules.gni

 # Copyright 2014 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.
 
 import("//base/android/linker/config.gni")
 import("//build/config/android/config.gni")
 import("//build/config/android/internal_rules.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/toolchain.gni")
 import("//third_party/android_platform/config.gni")
@@ skipping 1466 matching lines @@
       if (_load_library_from_apk) {
         defines += [ "ENABLE_CHROMIUM_LINKER_LIBRARY_IN_ZIP_FILE" ]
       }
       if (_enable_chromium_linker_tests) {
         defines += [ "ENABLE_CHROMIUM_LINKER_TESTS" ]
       }
     }
     _srcjar_deps += [ ":${_template_name}__native_libraries_java" ]
   }
 
+  if (!defined(invoker.apk_under_test)) {
+    java_cpp_template("${_template_name}__multidex_config_java") {
+      package_name = "org/chromium/base/multidex"
+      sources = [
+        "//base/android/java/templates/ChromiumMultiDex.template",
+      ]
+
+      defines = []
+      if (enable_multidex) {
+        defines += [ "ENABLE_MULTIDEX" ]
+      }
+    }
+    _srcjar_deps += [ ":${_template_name}__multidex_config_java" ]
+  }
+
   java_target = "${_template_name}__java"
   java_library_impl(java_target) {
     forward_variables_from(invoker, [ "run_findbugs" ])
     supports_android = true
     requires_android = true
     override_build_config = _build_config
     deps = _android_manifest_deps + [ ":$build_config_target" ]
 
     android_manifest = _android_manifest
     chromium_code = true
@@ skipping 760 matching lines @@
   }
 
   android_library(target_name) {
     java_files = []
     srcjar_deps = [ ":${_template_name}__protoc_java" ]
     deps = [
       "//third_party/android_protobuf:protobuf_nano_javalib",
     ]
   }
 }