[Extensions] Remove JSONFeatureProvider, SimpleFeature::Parse

extensions/common/features/manifest_feature.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/manifest_feature.h"
 
 #include "extensions/common/manifest.h"
 
 namespace extensions {
 
@@ skipping 16 matching lines @@
     return availability;
 
   // We know we can skip manifest()->GetKey() here because we just did the same
   // validation it would do above.
   if (extension && !extension->manifest()->value()->HasKey(name()))
     return CreateAvailability(NOT_PRESENT, extension->GetType());
 
   return CreateAvailability(IS_AVAILABLE);
 }
 
-bool ManifestFeature::Validate(std::string* error) {
-  if (!SimpleFeature::Validate(error))
-    return false;
-
-  if (extension_types().empty()) {
-    *error = name() + ": Manifest features must specify at least one " +
-             "value for extension_types.";
-    return false;
-  }
-
-  if (!contexts().empty()) {
-    *error = name() + ": Manifest features do not support contexts.";
-    return false;
-  }
-
-  return true;
-}
-
 }  // namespace extensions