Implement API features for the Extension API feature system

chrome/common/extensions/features/simple_feature.h

Index: chrome/common/extensions/features/simple_feature.h
diff --git a/chrome/common/extensions/features/simple_feature.h b/chrome/common/extensions/features/simple_feature.h
index 5b34c6e68f3269997a79ea6284f98bc374b3f993..4d1581d41afbf6beac41b23e7740f784c200f8ba 100644
--- a/chrome/common/extensions/features/simple_feature.h
+++ b/chrome/common/extensions/features/simple_feature.h
@@ -30,8 +30,9 @@ class SimpleFeature : public Feature {
 
   // Parses the JSON representation of a feature into the fields of this object.
   // Unspecified values in the JSON are not modified in the object. This allows
-  // us to implement inheritance by parsing one value after another.
-  void Parse(const DictionaryValue* value);
+  // us to implement inheritance by parsing one value after another. Returns
+  // the error found, or an empty string on success.
+  virtual std::string Parse(const DictionaryValue* value);
 
   // Returns true if the feature contains the same values as another.
   bool Equals(const SimpleFeature& other) const;