Add ClientConfig proto, and JSON generation/parsing.

components/data_reduction_proxy/proto/BUILD.gn

Index: components/data_reduction_proxy/proto/BUILD.gn
diff --git a/content/browser/notifications/BUILD.gn b/components/data_reduction_proxy/proto/BUILD.gn
similarity index 75%
copy from content/browser/notifications/BUILD.gn
copy to components/data_reduction_proxy/proto/BUILD.gn
index 0f6d5456988125873ebb894c8b61fe8383f46111..889c1067838d1e9f9de8724ac99dc15377ab540f 100644
--- a/content/browser/notifications/BUILD.gn
+++ b/components/data_reduction_proxy/proto/BUILD.gn
@@ -4,8 +4,8 @@
 
 import("//third_party/protobuf/proto_library.gni")
 
-proto_library("notification_proto") {
+proto_library("data_reduction_proxy_proto") {
   sources = [
-    "notification_database_data.proto",
+    "client_config.proto",
   ]
 }