Extensions: Only create Web request rules registry if Declarative Web Request is enabled.

extensions/common/features/feature.h

 // Copyright 2013 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.
 
 #ifndef EXTENSIONS_COMMON_FEATURES_FEATURE_H_
 #define EXTENSIONS_COMMON_FEATURES_FEATURE_H_
 
 #include <set>
 #include <string>
 
 #include "base/strings/string_piece.h"
 #include "base/values.h"
+#include "components/version_info/version_info.h"
 #include "extensions/common/manifest.h"
 
 class GURL;
 
 namespace extensions {
 
 class Extension;
 
 // Represents a single feature accessible to an extension developer, such as a
 // top-level manifest key, a permission, or a programmatic API. A feature can
@@ skipping 106 matching lines @@
   Availability IsAvailableToContext(const Extension* extension,
                                     Context context,
                                     const GURL& url) const {
     return IsAvailableToContext(extension, context, url, GetCurrentPlatform());
   }
   virtual Availability IsAvailableToContext(const Extension* extension,
                                             Context context,
                                             const GURL& url,
                                             Platform platform) const = 0;
 
+  // Returns the availability of the feature on the given |channel|. The
+  // availability result will either be IS_AVAILABLE, UNSUPPORTED_CHANNEL or
+  // NOT_PRESENT.
+  virtual Availability IsAvailableToChannel(

[karandeepb, 2017/02/17 02:07:57]

I couldn't find an existing way to check if an API is available on a channel.
There is IsAvailableToEnvironment, but I don't think it works correctly (Not
even sure what it is intended for, it has no actual callers, except tests).

+      version_info::Channel channel) const = 0;
+
   // Returns true if the feature is available to the current environment,
   // without needing to know information about an Extension or any other
   // contextual information. Typically used when the Feature is purely
   // configured by command line flags and/or Chrome channel.
   //
   // Generally try not to use this function. Even if you don't think a Feature
   // relies on an Extension now - maybe it will, one day, so if there's an
   // Extension available (or a runtime context, etc) then use the more targeted
   // method instead.
   Availability IsAvailableToEnvironment() const;
 
   virtual bool IsIdInBlacklist(const std::string& extension_id) const = 0;
   virtual bool IsIdInWhitelist(const std::string& extension_id) const = 0;
 
  protected:
   std::string name_;
   std::string alias_;
   std::string source_;
   bool no_parent_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_FEATURES_FEATURE_H_