[Extensions] Add a SimpleFeature::Validate function

extensions/common/features/json_feature_provider.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "extensions/common/features/json_feature_provider.h"
 
 #include <stddef.h>
 
 #include <stack>
 #include <utility>
@@ skipping 17 matching lines @@
   } else {
     // "nocompile" is not supported for any other feature type.
   }
   return nocompile;
 }
 
 bool ParseFeature(const base::DictionaryValue* value,
                   const std::string& name,
                   SimpleFeature* feature) {
   feature->set_name(name);
-  std::string error = feature->Parse(value);
-  if (!error.empty())
+  feature->Parse(value);
+  std::string error;
+  bool valid = feature->Validate(&error);
+  if (!valid)
     LOG(ERROR) << error;
-  return error.empty();
+  return valid;
 }
 
 }  // namespace
 
 JSONFeatureProvider::JSONFeatureProvider(const base::DictionaryValue& root,
                                          FeatureFactory factory)
     : factory_(factory) {
   for (base::DictionaryValue::Iterator iter(root); !iter.IsAtEnd();
        iter.Advance()) {
     if (IsNocompile(iter.value())) {
@@ skipping 88 matching lines @@
     } else {
       LOG(ERROR) << iter.key() << ": Feature description must be dictionary or"
                  << " list of dictionaries.";
     }
   }
 }
 
 JSONFeatureProvider::~JSONFeatureProvider() {}
 
 }  // namespace extensions