api: android.GetLatestBuild: re-support android_build_branch param

This adds back support for specifying which Android branch to look up.
The android_package param remains required.

BUG=b:259008604
TEST=run_tests
TEST=./api/contrib/call_scripts/android__get_latest_build

Change-Id: If045a4ec7e5248b45de43b219a36d111d36f7f0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4025568
Tested-by: Shao-Chuan Lee <shaochuan@chromium.org>
Auto-Submit: Shao-Chuan Lee <shaochuan@chromium.org>
Reviewed-by: Kazuhiro Inaba <kinaba@chromium.org>
Reviewed-by: Jack Neus <jackneus@google.com>
Commit-Queue: Jack Neus <jackneus@google.com>
diff --git a/api/controller/android.py b/api/controller/android.py
index 5047ef9..01dd13e 100644
--- a/api/controller/android.py
+++ b/api/controller/android.py
@@ -44,7 +44,10 @@
 @validate.require("android_package")
 @validate.validation_complete
 def GetLatestBuild(input_proto, output_proto, _config):
-    build_id, _ = android.GetLatestBuild(input_proto.android_package)
+    build_id, _ = android.GetLatestBuild(
+        input_proto.android_package,
+        build_branch=input_proto.android_build_branch,
+    )
     output_proto.android_version = build_id