Add tools to build Dart with Chromium's sysroot.

tools/set_x64_sysroot.sh

Index: tools/set_x64_sysroot.sh
diff --git a/tools/set_x64_sysroot.sh b/tools/set_x64_sysroot.sh
new file mode 100755
index 0000000000000000000000000000000000000000..bc28961ce609c54c2e85f8174f0f959e89812768
--- /dev/null
+++ b/tools/set_x64_sysroot.sh
@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+
+# Sets the compiler environment variables to use a downloaded wheezy sysroot
+# when building Dart with architecture x64.
+# Run this in the same working directory that you have run 
+# sdk/tools/download_chromium_sysroot.sh in.
+# Must be sourced, not run in a subshell, to modify the environment.
+# Run with the command ". sdk/tools/set_x64_sysroot.sh"
+# Only tested and used on Ubuntu trusty linux. Used to build dart with
+# no requirement for glibc greater than version 2.14.
+
+export CXXFLAGS="--sysroot=$PWD/build/linux/debian_wheezy_amd64-sysroot -I=/usr/include/c++/4.6 -I=/usr/include/c++/4.6/x86_64-linux-gnu"
+
+export LDFLAGS=--sysroot=$PWD/build/linux/debian_wheezy_amd64-sysroot
+export CFLAGS=--sysroot=$PWD/build/linux/debian_wheezy_amd64-sysroot