Introduce dart_host_toolchain arg, remove '--checked' option from patch_sdk.py

utils/kernel-service/BUILD.gn

Index: utils/kernel-service/BUILD.gn
diff --git a/utils/kernel-service/BUILD.gn b/utils/kernel-service/BUILD.gn
index f62e0642a82985e186720872b98dd5bf15723466..88ef85a351490e18ffc7e96eb412bac12092eb98 100644
--- a/utils/kernel-service/BUILD.gn
+++ b/utils/kernel-service/BUILD.gn
@@ -3,11 +3,12 @@
 # BSD-style license that can be found in the LICENSE file.
 
 import("../application_snapshot.gni")
+import("../../build/dart_host_toolchain.gni")
 
 application_snapshot("kernel-service") {
   dfe_script = "kernel-service.dart"
   deps = [
-    "../../runtime/vm:patched_sdk($host_toolchain)",
+    "../../runtime/vm:patched_sdk($dart_host_toolchain)",
   ]
   main_dart = dfe_script
   training_args = [