[Android] Support compiling with NDK r13b.

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) {
   import("//build_overrides/build.gni")
 
   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"
     default_android_ndk_version = "r12b"
-    default_android_ndk_major_version = "12"
+    default_android_ndk_major_version = 12
   } else {
     assert(defined(default_android_ndk_version))
     assert(defined(default_android_ndk_major_version))
   }
 
   if (!defined(default_android_sdk_root)) {
     default_android_sdk_root = "//third_party/android_tools/sdk"
     default_android_sdk_version = "24"
     default_android_sdk_build_tools_version = "24.0.2"
   }
@@ skipping 308 matching lines @@
           "//build/toolchain/android:android_${android_secondary_abi_cpu}"
     }
   }
 }
 
 declare_args() {
   # Enables used resource whitelist generation. Set for official builds only
   # as a large amount of build output is generated.
   enable_resource_whitelist_generation = is_android && is_official_build
 }