[Android] Make android_ndk_root configurable.

build/config/android/config.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.
 
 # This file contains common system config stuff for the Android build.
 
 if (is_android) {
   assert(rebase_path("//", root_build_dir) == "../../",
          "Android output directory must be nested 2 levels within src/ (" +
              "e.g.: out-gn/Debug). http://crbug.com/412935")
   has_chrome_android_internal =
       exec_script("//build/dir_exists.py",
                   [ rebase_path("//clank", root_build_dir) ],
                   "string") == "True"
 
   if (has_chrome_android_internal) {
     import("//clank/config.gni")
   }
 
   if (!defined(extra_chrome_shared_library_configs)) {
     extra_chrome_shared_library_configs = []
   }
 
+  if (!defined(default_android_ndk_root)) {
+    default_android_ndk_root = "//third_party/android_tools/ndk"
+  }
+
   if (!defined(default_android_sdk_root)) {
     default_android_sdk_root = "//third_party/android_tools/sdk"
     default_android_sdk_version = "23"
     default_android_sdk_build_tools_version = "23.0.1"
   }
 
   if (!defined(default_android_keystore_path)) {
     default_android_keystore_path =
         "//build/android/ant/chromium-debug.keystore"
     default_android_keystore_name = "chromiumdebugkey"
@@ skipping 10 matching lines @@
         "//third_party/android_tools:google_play_services_default_resources"
   }
 
   webview_public_framework_jar =
       "//third_party/android_platform/webview/frameworks_6.0.jar"
   if (!defined(webview_framework_jar)) {
     webview_framework_jar = webview_public_framework_jar
   }
 
   declare_args() {
+    android_ndk_root = default_android_ndk_root
+
     android_sdk_root = default_android_sdk_root
     android_sdk_version = default_android_sdk_version
     android_sdk_build_tools_version = default_android_sdk_build_tools_version
 
     # Libc++ library directory. Override to use a custom libc++ binary.
     android_libcpp_lib_dir = ""
 
     # Android versionCode for android_apk()s that don't expclitly set one.
     android_default_version_code = "1"
 
@@ skipping 76 matching lines @@
 
   # Directories and files ------------------------------------------------------
   #
   # We define may of the dirs strings here for each output architecture (rather
   # than just the current one) since these are needed by the Android toolchain
   # file to define toolchains for all possible targets in one pass.
 
   android_sdk = "${android_sdk_root}/platforms/android-${android_sdk_version}"
 
   # Path to the Android NDK and SDK.
-  android_ndk_root = "//third_party/android_tools/ndk"
   android_ndk_include_dir = "$android_ndk_root/usr/include"
 
   android_sdk_tools = "${android_sdk_root}/tools"
   android_sdk_build_tools =
       "${android_sdk_root}/build-tools/$android_sdk_build_tools_version"
 
   # Path to the SDK's android.jar
   android_sdk_jar = "$android_sdk/android.jar"
 
   zipalign_path = "$android_sdk_build_tools/zipalign"
@@ skipping 97 matching lines @@
   } else if (current_cpu == "mips64el") {
     android_app_abi = "mips64"
   } else {
     assert(false, "Unknown Android ABI: " + current_cpu)
   }
 
   if (android_libcpp_lib_dir == "") {
     android_libcpp_lib_dir = "${android_libcpp_root}/libs/${android_app_abi}"
   }
 }