Make the root_namespace argument to json_schema_compiler.gypi a string

chrome/common/extensions/api/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("//build/config/features.gni")
 import("//extensions/generated_extensions_api.gni")
 
 gypi_values = exec_script(
     "//build/gypi_to_gn.py",
     [ rebase_path("api.gyp") ],
@@ skipping 17 matching lines @@
     if (enable_webrtc) {
       sources += gypi_values.webrtc_schema_files
     }
   }
 
   if (!is_android) {
     uncompiled_sources = gypi_values.main_non_compiled_schema_files
   }
 
   impl_dir = "//chrome/browser/extensions/api"
-  root_namespace = "extensions::api"
+  root_namespace = "extensions::api::%(namespace)s"
   bundle = true
 
   deps = [
     # Different APIs include some headers from chrome/common that in turn
     # include generated headers from these targets.
     # TODO(brettw) this should be made unnecessary if possible.
     "//components/metrics/proto",
 
     "//content/public/browser",
     "//skia",
     "//sync",
   ]
   if (is_chromeos) {
     # deps += [ "<(DEPTH)/chrome/chrome.gyp:drive_proto" ]  TODO)GYP)
   }
 }