Add GN build support for Android 64-bit platforms.

build/config/sysroot.gni

 # Copyright (c) 2013 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 header file defines the "sysroot" variable which is the absolute path
 # of the sysroot. If no sysroot applies, the variable will be an empty string.
 
 declare_args() {
   # The absolute path of the sysroot that is applied when compiling using
   # the target toolchain.
   target_sysroot = ""
 }
 
 if (current_toolchain == default_toolchain && target_sysroot != "") {
   sysroot = target_sysroot
 } else if (is_android) {
   import("//build/config/android/config.gni")
   if (!is_android_webview_build) {
     if (cpu_arch == "x86") {
       sysroot = rebase_path("$android_ndk_root/$x86_android_sysroot_subdir")
     } else if (cpu_arch == "arm") {
       sysroot = rebase_path("$android_ndk_root/$arm_android_sysroot_subdir")
     } else if (cpu_arch == "mipsel") {
       sysroot = rebase_path("$android_ndk_root/$mips_android_sysroot_subdir")
+    } else if (cpu_arch == "x64") {
+      sysroot = rebase_path("$android_ndk_root/$x86_64_android_sysroot_subdir")
+    } else if (cpu_arch == "arm64") {
+      sysroot = rebase_path("$android_ndk_root/$arm64_android_sysroot_subdir")
+    } else if (cpu_arch == "mips64") {
+      sysroot = rebase_path("$android_ndk_root/$mips64_android_sysroot_subdir")
     } else {
       sysroot = ""
     }
   } else {
     sysroot = ""
   }
 } else if (is_linux && is_chrome_branded && is_official_build && !is_chromeos) {
   # For official builds, use the sysroot checked into the internal source repo
   # so that the builds work on older versions of Linux.
   if (cpu_arch == "x64") {
@@ skipping 14 matching lines @@
 } else if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
 
   sysroot = mac_sdk_path
 } else if (is_ios) {
   import("//build/config/ios/ios_sdk.gni")
   sysroot = ios_sdk_path
 } else {
   sysroot = ""
 }