Add GN build support for Android 64-bit platforms.

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) {
   has_chrome_android_internal =
       exec_script("//build/dir_exists.py",
                   [ rebase_path("//clank", root_build_dir) ],
@@ skipping 75 matching lines @@
 
   # Subdirectories inside android_ndk_root that contain the sysroot for the
   # associated platform.
   _android_api_level = 14
   x86_android_sysroot_subdir =
       "platforms/android-${_android_api_level}/arch-x86"
   arm_android_sysroot_subdir =
       "platforms/android-${_android_api_level}/arch-arm"
   mips_android_sysroot_subdir =
       "platforms/android-${_android_api_level}/arch-mips"
+  _android64_api_level = 21
+  x86_64_android_sysroot_subdir =
+      "platforms/android-${_android64_api_level}/arch-x86_64"
+  arm64_android_sysroot_subdir =
+      "platforms/android-${_android64_api_level}/arch-arm64"
+  mips64_android_sysroot_subdir =
+      "platforms/android-${_android64_api_level}/arch-mips64"
 
   # Toolchain root directory for each build. The actual binaries are inside
   # a "bin" directory inside of these.
   _android_toolchain_version = "4.9"
   x86_android_toolchain_root = "$android_ndk_root/toolchains/x86-${_android_toolchain_version}/prebuilt/${android_host_os}-${android_host_arch}"
   arm_android_toolchain_root = "$android_ndk_root/toolchains/arm-linux-androideabi-${_android_toolchain_version}/prebuilt/${android_host_os}-${android_host_arch}"
   mips_android_toolchain_root = "$android_ndk_root/toolchains/mipsel-linux-android-${_android_toolchain_version}/prebuilt/${android_host_os}-${android_host_arch}"
+  x86_64_android_toolchain_root = "$android_ndk_root/toolchains/x86_64-${_android_toolchain_version}/prebuilt/${android_host_os}-${android_host_arch}"
+  arm64_android_toolchain_root = "$android_ndk_root/toolchains/aarch64-${_android_toolchain_version}/prebuilt/${android_host_os}-${android_host_arch}"
+  mips64_android_toolchain_root = "$android_ndk_root/toolchains/mips64el-${_android_toolchain_version}/prebuilt/${android_host_os}-${android_host_arch}"
 
   # Location of libgcc. This is only needed for the current GN toolchain, so we
   # only need to define the current one, rather than one for every platform
   # like the toolchain roots.
   if (cpu_arch == "x86") {
     android_prebuilt_arch = "android-x86"
     _binary_prefix = "i686-linux-android"
     android_toolchain_root = "$x86_android_toolchain_root"
     android_libgcc_file = "$android_toolchain_root/lib/gcc/i686-linux-android/${_android_toolchain_version}/libgcc.a"
   } else if (cpu_arch == "arm") {
     android_prebuilt_arch = "android-arm"
     _binary_prefix = "arm-linux-androideabi"
     android_toolchain_root = "$arm_android_toolchain_root"
     android_libgcc_file = "$android_toolchain_root/lib/gcc/arm-linux-androideabi/${_android_toolchain_version}/libgcc.a"
   } else if (cpu_arch == "mipsel") {
     android_prebuilt_arch = "android-mips"
     _binary_prefix = "mipsel-linux-android"
     android_toolchain_root = "$mips_android_toolchain_root"
     android_libgcc_file = "$android_toolchain_root/lib/gcc/mipsel-linux-android/${_android_toolchain_version}/libgcc.a"
+  } else if (cpu_arch == "x64") {
+    android_prebuilt_arch = "android-x86_64"
+    _binary_prefix = "x86_64-linux-android"
+    android_toolchain_root = "$x86_64_android_toolchain_root"
+    android_libgcc_file = "$android_toolchain_root/lib/gcc/x86_64-linux-android/${_android_toolchain_version}/libgcc.a"
+  } else if (cpu_arch == "arm64") {
+    android_prebuilt_arch = "android-arm64"
+    _binary_prefix = "aarch64-linux-android"
+    android_toolchain_root = "$arm64_android_toolchain_root"
+    android_libgcc_file = "$android_toolchain_root/lib/gcc/aarch64-linux-android/${_android_toolchain_version}/libgcc.a"
+  } else if (cpu_arch == "mips64el") {
+    android_prebuilt_arch = "android-mips64"
+    _binary_prefix = "mips64el-linux-android"
+    android_toolchain_root = "$mips64_android_toolchain_root"
+    android_libgcc_file = "$android_toolchain_root/lib/gcc/mips64el-linux-android/${_android_toolchain_version}/libgcc.a"
   } else {
     assert(false, "Need android libgcc support for your target arch.")
   }
 
   android_tool_prefix = "$android_toolchain_root/bin/$_binary_prefix-"
   android_readelf = "${android_tool_prefix}readelf"
   android_objcopy = "${android_tool_prefix}objcopy"
   android_gdbserver =
       "$android_ndk_root/prebuilt/$android_prebuilt_arch/gdbserver/gdbserver"
 
@@ skipping 11 matching lines @@
     android_app_abi = "x86"
   } else if (cpu_arch == "arm") {
     import("//build/config/arm.gni")
     if (arm_version < 7) {
       android_app_abi = "armeabi"
     } else {
       android_app_abi = "armeabi-v7a"
     }
   } else if (cpu_arch == "mipsel") {
     android_app_abi = "mips"
+  } else if (cpu_arch == "x64") {
+    android_app_abi = "x86_64"
+  } else if (cpu_arch == "arm64") {
+    android_app_abi = "arm64-v8a"
+  } else if (cpu_arch == "mips64el") {
+    android_app_abi = "mips64"
   } else {
     assert(false, "Unknown Android ABI: " + cpu_arch)
   }
 } else {
   if (!defined(is_android_webview_build)) {
     is_android_webview_build = false
   }
 }