[Android] Add gyp support for multidex.

build/secondary/third_party/android_tools/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/android/rules.gni")
 
 config("cpu_features_include") {
   include_dirs = [ "ndk/sources/android/cpufeatures" ]
 }
 
@@ skipping 31 matching lines @@
 }
 
 android_java_prebuilt("android_support_design_java") {
   deps = [
     ":android_support_v7_appcompat_java",
     ":android_support_design_resources",
   ]
   jar_path = "$android_sdk_root/extras/android/support/design/libs/android-support-design.jar"
 }
 
+java_prebuilt("android_support_multidex_java") {
+  supports_android = true
+  jar_path = "$android_sdk_root/extras/android/support/multidex/library/libs/android-support-multidex.jar"
+}
+
 android_java_prebuilt("android_support_v13_java") {
   jar_path =
       "$android_sdk_root/extras/android/support/v13/android-support-v13.jar"
 }
 
 android_resources("android_support_v7_appcompat_resources") {
   v14_skip = true
   resource_dirs =
       [ "$android_sdk_root/extras/android/support/v7/appcompat/res" ]
   custom_package = "android.support.v7.appcompat"
@@ skipping 70 matching lines @@
     rebase_path("$target_gen_dir/checked_sdk_extras_version.stamp"),
   ]
   inputs = [
     "//build/android_sdk_extras.json",
     "$android_sdk_root/extras/google/google_play_services/source.properties",
   ]
   outputs = [
     "$target_gen_dir/checked_sdk_extras_version.stamp",
   ]
 }