Add ClientConfig proto, and JSON generation/parsing.

components/data_reduction_proxy/core/common/data_reduction_proxy_params.h

Index: components/data_reduction_proxy/core/common/data_reduction_proxy_params.h
diff --git a/components/data_reduction_proxy/core/common/data_reduction_proxy_params.h b/components/data_reduction_proxy/core/common/data_reduction_proxy_params.h
index 256c6c4ef8bd399a88b0252fef9d3bd3422d63eb..30c51ff7bc5f7daa825b0f39aa2ce0487b31891f 100644
--- a/components/data_reduction_proxy/core/common/data_reduction_proxy_params.h
+++ b/components/data_reduction_proxy/core/common/data_reduction_proxy_params.h
@@ -13,6 +13,7 @@
 #include "url/gurl.h"
 
 namespace base {
+class DictionaryValue;
 class TimeDelta;
 }
 
@@ -131,6 +132,10 @@ class DataReductionProxyParams : public DataReductionProxyConfigValues {
   // If true, uses QUIC instead of SPDY to connect to proxies that use TLS.
   void EnableQuic(bool enable);
 
+  // Populates |response| with the Data Reduction Proxy server configuration.
+  // Virtual for mocking.
+  virtual void PopulateConfigResponse(base::DictionaryValue* response) const;
+
   // Overrides of |DataReductionProxyConfigValues|
   bool UsingHTTPTunnel(const net::HostPortPair& proxy_server) const override;