Cleanup and simplify HostConfig and JsonHostConfig.

remoting/host/host_key_pair.cc

Index: remoting/host/host_key_pair.cc
diff --git a/remoting/host/host_key_pair.cc b/remoting/host/host_key_pair.cc
index 7bf1e843a516bdde8b3a4a92d7da782140cb84dc..704f8f88c4745fc5b42a5caf11c0652bfa917e01 100644
--- a/remoting/host/host_key_pair.cc
+++ b/remoting/host/host_key_pair.cc
@@ -44,9 +44,9 @@ bool HostKeyPair::LoadFromString(const std::string& key_base64) {
   return true;
 }
 
-bool HostKeyPair::Load(HostConfig* host_config) {
+bool HostKeyPair::Load(const HostConfig& host_config) {
   std::string key_base64;
-  if (!host_config->GetString(kPrivateKeyConfigPath, &key_base64)) {
+  if (!host_config.GetString(kPrivateKeyConfigPath, &key_base64)) {
     LOG(ERROR) << "Private key wasn't found in the config file.";
     return false;
   }