[Android] Rework multidex and enable multidex for unit_tests_apk.

chrome/test/BUILD.gn

 # 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("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/chrome_tests.gni")
@@ skipping 1626 matching lines @@
             "//chrome")
     deps += [
       ":unit_tests_java",
       "//components/offline_pages:test_support",
       "//v8:v8_external_startup_data_assets",
     ]
     deps -= [ "//third_party/libaddressinput" ]
 
     android_manifest =
         "//chrome/test/android/unit_tests_apk/AndroidManifest.xml"
+    enable_multidex = true
     isolate_file = "../unit_tests.isolate"
 
     # Some android targets still depend on --gc-sections to link.
     # TODO: remove --gc-sections for Debug builds (crbug.com/159847).
     ldflags = [ "-Wl,--gc-sections" ]
   } else {
     sources += rebase_path(
             chrome_tests_unit_gypi_values.chrome_unit_tests_non_android_sources,
             ".",
             "//chrome")
@@ skipping 586 matching lines @@
 if (is_android) {
   android_library("unit_tests_java") {
     DEPRECATED_java_in_dir = "//chrome/test/android/unit_tests_apk/src"
     deps = [
       "//base:base_java",
       "//chrome/android:chrome_java",
       "//content/public/android:content_java",
     ]
   }
 }