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

extensions/common/features/feature.h

Index: extensions/common/features/feature.h
diff --git a/extensions/common/features/feature.h b/extensions/common/features/feature.h
index d3179bb9b2a21b40a75ddc808f05296699275590..0664e1737f04e3f7f2eb738183a971a3e2b1f7d7 100644
--- a/extensions/common/features/feature.h
+++ b/extensions/common/features/feature.h
@@ -10,6 +10,7 @@
 
 #include "base/strings/string_piece.h"
 #include "base/values.h"
+#include "components/version_info/version_info.h"
 #include "extensions/common/manifest.h"
 
 class GURL;
@@ -136,6 +137,12 @@ class Feature {
                                             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