Add cloud_devices and json_schema to GN build.

components/json_schema/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.
 
-source_set("language_usage_metrics") {
+static_library("json_schema") {
   sources = [
-    "language_usage_metrics.cc",
-    "language_usage_metrics.h",
+    "json_schema_constants.cc",
+    "json_schema_constants.h",
+    "json_schema_validator.cc",
+    "json_schema_validator.h",
   ]
 
   deps = [
     "//base",
+    "//third_party/re2",
   ]
 }