Add cloud_devices and json_schema to GN build.

components/json_schema/BUILD.gn

Index: components/json_schema/BUILD.gn
diff --git a/components/language_usage_metrics/BUILD.gn b/components/json_schema/BUILD.gn
similarity index 53%
copy from components/language_usage_metrics/BUILD.gn
copy to components/json_schema/BUILD.gn
index 88ad430bd5d7fa51b30734c134e38914e8ab72cd..8bcb7d52e62af3782ab062cc0bd5e962d3901a32 100644
--- a/components/language_usage_metrics/BUILD.gn
+++ b/components/json_schema/BUILD.gn
@@ -2,13 +2,16 @@
 # 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",
   ]
 }