GN: Add an option to build against the Debian wheezy sysroot

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 = ""
+
+  # Whether the Debian wheezy sysroot should be used.
+  dart_use_wheezy_sysroot = false
+}
+
+if (is_linux && dart_use_wheezy_sysroot) {
+  if (current_cpu == "x86") {
+    target_sysroot = rebase_path("//build/linux/debian_wheezy_i386-sysroot")
+  } else if (current_cpu == "x64") {
+    target_sysroot = rebase_path("//build/linux/debian_wheezy_amd64-sysroot")
+  } else {
+    print("There is no Debian wheezy sysroot present for $current_cpu")
+    assert(false)
+  }
 }
 
 if (current_toolchain == default_toolchain && target_sysroot != "") {
   sysroot = target_sysroot
 } else if (is_android) {
   import("//build/config/android/config.gni")
   if (current_cpu == "x86") {
     sysroot = rebase_path("$android_ndk_root/$x86_android_sysroot_subdir")
   } else if (current_cpu == "arm") {
     sysroot = rebase_path("$android_ndk_root/$arm_android_sysroot_subdir")
   } else if (current_cpu == "mipsel") {
     sysroot = rebase_path("$android_ndk_root/$mips_android_sysroot_subdir")
   } else if (current_cpu == "x64") {
     sysroot = rebase_path("$android_ndk_root/$x86_64_android_sysroot_subdir")
   } else if (current_cpu == "arm64") {
     sysroot = rebase_path("$android_ndk_root/$arm64_android_sysroot_subdir")
   } else if (current_cpu == "mips64") {
     sysroot = rebase_path("$android_ndk_root/$mips64_android_sysroot_subdir")
   } else {
     sysroot = ""
   }
 } else if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
   sysroot = mac_sdk_path
 } else {
   sysroot = ""
 }