coverage: Update rust_coverage USE flag if set.

At present, we do not generate coverage for rust packages and we need to
use a different USE flag to generate code coverage for rust packages.
Accept a new field and add that USE flag when rust_code_coverage is set
in the request.

BUG=b:246409134
TEST=./run_tests service/test_unittests.py

Cq-Depend: chromium:3892792
Change-Id: Iabd4c2b6ff81ab06bd9aa404c484244ed2ae15d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3892108
Reviewed-by: Cindy Lin <xcl@google.com>
Tested-by: Srinivas Hegde <srinivashegde@google.com>
Commit-Queue: Srinivas Hegde <srinivashegde@google.com>
diff --git a/api/controller/test.py b/api/controller/test.py
index 1c007b4..bb37ea2 100644
--- a/api/controller/test.py
+++ b/api/controller/test.py
@@ -116,6 +116,7 @@
     build_target = controller_util.ParseBuildTarget(input_proto.build_target)
 
     code_coverage = input_proto.flags.code_coverage
+    rust_code_coverage = input_proto.flags.rust_code_coverage
 
     sysroot = sysroot_lib.Sysroot(build_target.root)
 
@@ -125,6 +126,7 @@
         blocklist=blocklist,
         was_built=was_built,
         code_coverage=code_coverage,
+        rust_code_coverage=rust_code_coverage,
         testable_packages_optional=testable_packages_optional,
         filter_only_cros_workon=filter_only_cros_workon,
     )