depot_tools: expose path to download_from_google_storage

BUG=585401

Review URL: https://codereview.chromium.org/1770383004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299158 0039d316-1c4b-4281-b951-d872f2087c98

recipe_modules/depot_tools/api.py

+# Copyright 2016 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.
+
+from recipe_engine import recipe_api
+
+class DepotToolsApi(recipe_api.RecipeApi):
+  @property
+  def download_from_google_storage_path(self):
+    return self.package_resource('download_from_google_storage.py')