Add wrapper shell script to invoke dartk with checked-in binary

tools/dartk_wrappers/dartk

Index: tools/dartk_wrappers/dartk
diff --git a/tools/dartk_wrappers/dartk b/tools/dartk_wrappers/dartk
new file mode 100755
index 0000000000000000000000000000000000000000..ca93a28050513fc31f07acea94c2226c7d7459ba
--- /dev/null
+++ b/tools/dartk_wrappers/dartk
@@ -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.
+
+# Unlike $0, $BASH_SOURCE points to the absolute path of this file.
+PROG_NAME="$BASH_SOURCE"
+WRAPPERS_DIR="$(cd "${PROG_NAME%/*}" ; pwd -P)"
+DART_ROOT="$(cd "${WRAPPERS_DIR}/../.." ; pwd -P)"
+DARTK="$DART_ROOT/third_party/pkg/kernel/bin/dartk.dart"
+
+if [[ `uname` == 'Darwin' ]];
+then
+  DART="$DART_ROOT/tools/sdks/mac/dart-sdk/bin/dart"
+else
+  DART="$DART_ROOT/tools/sdks/linux/dart-sdk/bin/dart"
+fi
+
+exec "$DART" "$DARTK" "$@"