Convert tabs, windows, and extension APIs to feature system.

chrome/common/extensions/feature.h

Index: chrome/common/extensions/feature.h
diff --git a/chrome/common/extensions/feature.h b/chrome/common/extensions/feature.h
index 374767055efe108258c92cb676e9402e0d474749..a6043691292796994724ddc5149fa12c4838f288 100644
--- a/chrome/common/extensions/feature.h
+++ b/chrome/common/extensions/feature.h
@@ -101,11 +101,14 @@ class 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);
+  virtual void Parse(const DictionaryValue* value);
 
   // Returns true if the feature contains the same values as another.
   bool Equals(const Feature& other) const;
 
+  // Returns true if the Feature contains no special configuration.
+  bool IsEmpty() const;
+
   // Returns true if the feature is available to be parsed into a new extension
   // manifest.
   Availability IsAvailableToManifest(const std::string& extension_id,
@@ -134,6 +137,11 @@ class Feature {
   // Returns an error message for an Availability code.
   std::string GetErrorMessage(Availability result);
 
+ protected:
+  static void ParseSet(const DictionaryValue* value,
+                       const std::string& property,
+                       std::set<std::string>* set);
+
  private:
   std::string name_;