[Extensions Bindings] Add a bindings/ subdirectory under renderer

extensions/renderer/bindings/api_signature.h

 // Copyright 2016 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_RENDERER_API_SIGNATURE_H_
-#define EXTENSIONS_RENDERER_API_SIGNATURE_H_
+#ifndef EXTENSIONS_RENDERER_BINDINGS_API_SIGNATURE_H_
+#define EXTENSIONS_RENDERER_BINDINGS_API_SIGNATURE_H_
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "v8/include/v8.h"
 
 namespace base {
 class Value;
@@ skipping 53 matching lines @@
   std::vector<std::unique_ptr<ArgumentSpec>> signature_;
 
   // A developer-readable signature string, lazily set.
   mutable std::string expected_signature_;
 
   DISALLOW_COPY_AND_ASSIGN(APISignature);
 };
 
 }  // namespace extensions
 
-#endif  // EXTENSIONS_RENDERER_API_SIGNATURE_H_
+#endif  // EXTENSIONS_RENDERER_BINDINGS_API_SIGNATURE_H_