Break the circular dependency in the new mojom bindings generation pipeline.

mojo/public/python/BUILD.gn

 # Copyright 2014 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.
 
 import("../mojo_sdk.gni")
 import("//third_party/cython/rules.gni")
 import("rules.gni")
 
 group("python") {
   deps = [
@@ skipping 97 matching lines @@
   rebase_timestamp = rebase_path(timestamp, root_build_dir)
   args = [
     "--inputs=${rebase_inputs}",
     "--output=${rabase_output}",
     "--timestamp=${rebase_timestamp}",
   ]
 
   deps = mojom_deps
 }
 
-copy("bindings") {
+group("bindings") {
+  deps = [
+    ":import_interface_bindings",
+    ":serialization_bindings",
+  ]
+}
+
+# This target lists dependencies needed to use generated mojom files for
+# serialization/deserialization only, but not the full mojo application stack.
+copy("serialization_bindings") {
   sources = [
     "mojo_bindings/__init__.py",
     "mojo_bindings/descriptor.py",
     "mojo_bindings/interface_reflection.py",
     "mojo_bindings/messaging.py",
     "mojo_bindings/promise.py",
     "mojo_bindings/reflection.py",
     "mojo_bindings/serialization.py",
   ]
   outputs = [
     "$root_out_dir/python/mojo_bindings/{{source_file_part}}",
   ]
   deps = [
-    ":import_interface_bindings",
     ":mojo_system",
   ]
 }
 
 python_package("packaged_bindings") {
   sources = [
     "mojo_bindings/__init__.py",
     "mojo_bindings/descriptor.py",
     "mojo_bindings/interface_reflection.py",
     "mojo_bindings/messaging.py",
     "mojo_bindings/promise.py",
     "mojo_bindings/reflection.py",
     "mojo_bindings/serialization.py",
   ]
 
   deps = [
     "../interfaces/bindings:bindings_python",
   ]
 }