Generate the proto JSON converter for DOM distiller

third_party/protobuf/proto_library.gni

 # 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.
 
 # Compile a protocol buffer.
 #
 # Protobuf parameters:
 #
 #   proto_out_dir (optional)
 #       Specifies the path suffix that output files are generated under. This
@@ skipping 130 matching lines @@
     ]
 
     deps = [
       protoc_label,
     ]
 
     # The deps may have steps that have to run before runnign protobuf.
     if (defined(invoker.deps)) {
       deps += invoker.deps
     }
+
+    if (defined(invoker.json_converter)) {
+      args += [
+        "--plugin=protoc-gen-json_converter=" +
+            rebase_path(invoker.json_converter, root_build_dir),
+        "--json_converter_out=output_dir=:$rel_out_dir",

[dcheng, 2016/06/14 04:27:39]

Seems a bit weird to specify this here, maybe we can just have an
additional_args parameter?

Also, is it possible to pas more than one --plugin argument to protoc? It'd be
nice not to have to duplicate all the protoc_plugins.

[wychen, 2016/08/07 09:16:27]

Moving all the logic to dom_distiller_js/BUILD.gn can also work, but I'm trying
to make this work as a template for protoc plugins. I'm not sure how general
this is, since we are the first one using plugins here. The benefit of putting
the logic here is that it will be visible when there are more users of the
plugins in the future. If they happen to be using json_converter, then this can
work as is. For other kinds of plugins, we'll see how much of the logic can be
factored out when the time comes.

+      ]
+      outputs += [ "$out_dir/{{source_name_part}}_json_converter.h" ]
+    }
   }
 
   source_set(target_name) {
     forward_variables_from(invoker,
                            [
                              "visibility",
                              "defines",
                            ])
 
     sources = get_target_outputs(":$action_name")
@@ skipping 13 matching lines @@
       ":$action_name",
     ]
 
     # This will link any libraries in the deps (the use of invoker.deps in the
     # action won't link it).
     if (defined(invoker.deps)) {
       deps += invoker.deps
     }
   }
 }