[Android] Add gn support for multidex.

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/toolchain/toolchain.gni")
 import("//third_party/android_platform/config.gni")
 import("//tools/grit/grit_rule.gni")
@@ skipping 1212 matching lines @@
   gen_dir = "$target_gen_dir/$target_name"
   base_path = "$gen_dir/$target_name"
   _build_config = "$target_gen_dir/$target_name.build_config"
   resources_zip_path = "$base_path.resources.zip"
   _all_resources_zip_path = "$base_path.resources.all.zip"
   _jar_path = "$base_path.jar"
   _lib_dex_path = "$base_path.dex.jar"
   _rebased_lib_dex_path = rebase_path(_lib_dex_path, root_build_dir)
   _template_name = target_name
 
-  final_dex_path = "$gen_dir/classes.dex"
+  multidex = defined(invoker.multidex) && invoker.multidex
+  if (multidex) {
+    final_dex_path = "$gen_dir/classes.dex.zip"
+  } else {
+    final_dex_path = "$gen_dir/classes.dex"
+  }
   final_dex_target_name = "${_template_name}__final_dex"
 
   _final_apk_path = ""
   if (defined(invoker.final_apk_path)) {
     _final_apk_path = invoker.final_apk_path
   } else if (defined(invoker.apk_name)) {
     _final_apk_path = "$root_build_dir/apks/" + invoker.apk_name + ".apk"
   }
   _dist_jar_path_list =
       process_file_template(
@@ skipping 283 matching lines @@
       rebased_proguard_configs = rebase_path(_proguard_configs, root_build_dir)
       args = [
         "--proguard-configs=$rebased_proguard_configs",
         "--tested-apk-info=@FileArg($_rebased_build_config:proguard:tested_apk_info)",
         "--input-paths=@FileArg($_rebased_build_config:proguard:input_paths)",
       ]
     }
     _dex_sources = [ _proguard_jar_path ]
     _dex_deps = [ ":$_proguard_target" ]
   } else {
-    _dex_sources = [ _lib_dex_path ]
+    if (multidex) {
+      _dex_sources = [ _jar_path ]
+    } else {
+      _dex_sources = [ _lib_dex_path ]
+    }
     _dex_deps = [ ":$java_target" ]
   }
 
   dex("$final_dex_target_name") {
+    forward_variables_from(invoker, [ "multidex" ])
     deps = _dex_deps + [ ":$build_config_target" ]
     inputs = [
       _build_config,
     ]
     sources = _dex_sources
     output = final_dex_path
-    _dex_arg_key = "${_rebased_build_config}:final_dex:dependency_dex_files"
+    if (multidex) {
+      _dex_arg_key = "${_rebased_build_config}:dist_jar:dependency_jars"
+    } else {
+      _dex_arg_key = "${_rebased_build_config}:final_dex:dependency_dex_files"
+    }
     args = [ "--inputs=@FileArg($_dex_arg_key)" ]
   }
 
   if (_native_libs != []) {
     _prepare_native_target_name = "${_template_name}__prepare_native"
     action(_prepare_native_target_name) {
       forward_variables_from(invoker,
                              [
                                "data_deps",
                                "public_deps",
@@ skipping 591 matching lines @@
   }
 
   android_library(target_name) {
     java_files = []
     srcjar_deps = [ ":${_template_name}__protoc_java" ]
     deps = [
       "//third_party/android_protobuf:protobuf_nano_javalib",
     ]
   }
 }