Unbundle openh264

build/shim_headers.gni

 # Copyright 2016 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.
 
 template("shim_headers") {
   action_name = "gen_${target_name}"
   config_name = "${target_name}_config"
   shim_headers_path = "${root_gen_dir}/shim_headers/${target_name}"
 
   config(config_name) {
     include_dirs = [ shim_headers_path ]
   }
 
   action(action_name) {
     script = "//tools/generate_shim_headers/generate_shim_headers.py"
     args = [
-             "--generate",
-             "--headers-root",
-             rebase_path(invoker.root_path),
-             "--output-directory",
-             rebase_path(shim_headers_path),
-           ] + invoker.headers
+      "--generate",
+      "--headers-root",
+      rebase_path(invoker.root_path),
+      "--output-directory",
+      rebase_path(shim_headers_path),
+    ]
+    if (defined(invoker.prefix)) {
+      args += [
+        "--prefix",
+        invoker.prefix,
+      ]
+    }
+    args += invoker.headers
 
     outputs = process_file_template(invoker.headers,
                                     "${shim_headers_path}/{{source_file_part}}")
   }
 
   group(target_name) {
     deps = [
       ":${action_name}",
     ]
     all_dependent_configs = [ ":${config_name}" ]
   }
 }