Add gclient hook to download prebuilt mojo_shell

mojo/tools/upload_shell_binary.py

+#!/usr/bin/env python
+
+import os
+import subprocess
+import tempfile
+import time
+import zipfile
+
+root_path = os.path.join(os.path.dirname(os.path.realpath(__file__)),
+                            "..", "..")
+version_path = os.path.join(root_path, "mojo", "public", "VERSION")
+version_file = open(version_path)
+version = version_file.read().strip()
+
+binary_path = os.path.join(root_path, "out", "Release", "mojo_shell")
+
+dest = "gs://mojo/shell/" + version + "/linux-x64.zip"
+
+with tempfile.NamedTemporaryFile() as zip_file:
+  with zipfile.ZipFile(zip_file, 'w') as z:
+    with open(binary_path) as shell_binary:
+      zipinfo = zipfile.ZipInfo("mojo_shell")
+      zipinfo.external_attr = 0777 << 16L
+      zipinfo.compress_type = zipfile.ZIP_DEFLATED
+      zipinfo.date_time = time.gmtime(os.path.getmtime(binary_path))
+      z.writestr(zipinfo, shell_binary.read())
+  subprocess.check_call(["gsutil", "cp", zip_file.name, dest])