Implement API features for the Extension API feature system

chrome/common/extensions/features/manifest_feature.cc

 // Copyright (c) 2012 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 "chrome/common/extensions/features/manifest_feature.h"
 
 #include "chrome/common/extensions/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);
 }
 
+std::string ManifestFeature::Parse(const DictionaryValue* value) {
+  std::string error = SimpleFeature::Parse(value);
+  if (!error.empty())
+    return error;
+
+  if (extension_types()->empty()) {
+    return name() + ": Manifest features must specify at least one " +
+        "value for extension_types.";
+  }
+
+  if (!GetContexts()->empty())
+    return name() + ": Manifest features do not support contexts.";
+
+  return "";
+}
+
 }  // namespace