add PRESUBMIT for native_client_sdk.

native_client_sdk/src/build_tools/sdk_tools/sdk_update.py

Index: native_client_sdk/src/build_tools/sdk_tools/sdk_update.py
diff --git a/native_client_sdk/src/build_tools/sdk_tools/sdk_update.py b/native_client_sdk/src/build_tools/sdk_tools/sdk_update.py
index 1bfefe37927c90708f6de963070c0fe82aabf9ac..ac423a5e5d20787a5551d1813740bd34bc099309 100755
--- a/native_client_sdk/src/build_tools/sdk_tools/sdk_update.py
+++ b/native_client_sdk/src/build_tools/sdk_tools/sdk_update.py
@@ -3,13 +3,6 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import os
-import re
-import subprocess
-from sdk_update_common import *
-import sys
-import tempfile
-
 """Shim script for the SDK updater, to allow automatic updating.
 
 The purpose of this script is to be a shim which automatically updates
@@ -20,6 +13,12 @@ When the sdk_tools bundle has been updated to the most recent version, this
 script forwards its arguments to sdk_updater_main.py.
 """
 
+import os
+import subprocess
+from sdk_update_common import *
+import sys
+import tempfile
+
 
 SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
 SDK_UPDATE_MAIN = os.path.join(SCRIPT_DIR, 'sdk_update_main.py')