Add a check for server and CA certificates in device policies to the ONC validator.

chromeos/network/onc/onc_validator.h

Index: chromeos/network/onc/onc_validator.h
diff --git a/chromeos/network/onc/onc_validator.h b/chromeos/network/onc/onc_validator.h
index f928f3d823f517f556f0c299b3b6bf4a3a79b3d5..1de930b32b2cd3b06c1171e6f94d2f918e4b8cf2 100644
--- a/chromeos/network/onc/onc_validator.h
+++ b/chromeos/network/onc/onc_validator.h
@@ -210,6 +210,9 @@ class CHROMEOS_EXPORT Validator : public Mapper {
                                   int lower_bound,
                                   int upper_bound);
 
+  bool FieldExistsAndIsEmpty(const base::DictionaryValue& object,
+                             const std::string& field_name);
+
   bool RequireField(const base::DictionaryValue& dict, const std::string& key);
 
   bool CertPatternInDevicePolicy(const std::string& cert_type);