Implement API features for the Extension API feature system

chrome/common/extensions/features/feature.h

Index: chrome/common/extensions/features/feature.h
diff --git a/chrome/common/extensions/features/feature.h b/chrome/common/extensions/features/feature.h
index 53fa06bef270d2079d1fc49bb2976fc965043caf..bd7f8d11a841ae36336503911970e629df6157df 100644
--- a/chrome/common/extensions/features/feature.h
+++ b/chrome/common/extensions/features/feature.h
@@ -124,6 +124,7 @@ class Feature {
 
   const std::string& name() const { return name_; }
   void set_name(const std::string& name) { name_ = name; }
+  const std::set<std::string>& dependencies() { return dependencies_; }
 
   // Gets the platform the code is currently running on.
   static Platform GetCurrentPlatform();
@@ -167,6 +168,7 @@ class Feature {
 
  protected:
   std::string name_;
+  std::set<std::string> dependencies_;
 };
 
 }  // namespace extensions