sdk: convert docstring annotations

Converts Python docstring annotations to type hints.

BUG=b:196895668
TEST=./run_tests api/controller/sdk_unittest.py

Change-Id: I550de1c3a923ee5c0f456addf4d01bb8f3e0abed
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3661374
Commit-Queue: Kevin Shelton <kmshelton@chromium.org>
Commit-Queue: Alex Klein <saklein@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Auto-Submit: Kevin Shelton <kmshelton@chromium.org>
Tested-by: Kevin Shelton <kmshelton@chromium.org>
diff --git a/api/controller/sdk.py b/api/controller/sdk.py
index 8ef3103..06e4182 100644
--- a/api/controller/sdk.py
+++ b/api/controller/sdk.py
@@ -5,6 +5,7 @@
 """SDK chroot operations."""
 
 import os
+from typing import Union
 
 from chromite.api import controller
 from chromite.api import faux
@@ -21,13 +22,17 @@
 
 @faux.success(_ChrootVersionResponse)
 @faux.empty_error
-def Create(input_proto, output_proto, config):
+def Create(input_proto: 'CreateRequest', output_proto: 'CreateResponse',
+           config: 'api_config.ApiConfig') -> Union[int, None]:
   """Chroot creation, includes support for replacing an existing chroot.
 
   Args:
-    input_proto (CreateRequest): The input proto.
-    output_proto (CreateResponse): The output proto.
-    config (api_config.ApiConfig): The API call config.
+    input_proto: The input proto.
+    output_proto: The output proto.
+    config: The API call config.
+
+  Returns:
+    An error code, None otherwise.
   """
   replace = not input_proto.flags.no_replace
   bootstrap = input_proto.flags.bootstrap
@@ -65,13 +70,14 @@
 @faux.empty_error
 @validate.require_each('toolchain_targets', ['name'])
 @validate.validation_complete
-def Update(input_proto, output_proto, _config):
+def Update(input_proto: 'UpdateRequest', output_proto: 'UpdateResponse',
+           _config: 'api_config.ApiConfig'):
   """Update the chroot.
 
   Args:
-    input_proto (UpdateRequest): The input proto.
-    output_proto (UpdateResponse): The output proto.
-    _config (api_config.ApiConfig): The API call config.
+    input_proto: The input proto.
+    output_proto: The output proto.
+    _config: The API call config.
   """
   build_source = input_proto.flags.build_source
   targets = [target.name for target in input_proto.toolchain_targets]