[Extensions Binding] Allow for registering custom hooks

extensions/renderer/api_binding_types.h

Index: extensions/renderer/api_binding_types.h
diff --git a/extensions/renderer/api_binding_types.h b/extensions/renderer/api_binding_types.h
index 447bb59e2c9a04af1c5bf5a17b6990d46ef08392..d5c9af5067f8e49cf07b60b03703e1f47a7c9ada 100644
--- a/extensions/renderer/api_binding_types.h
+++ b/extensions/renderer/api_binding_types.h
@@ -5,10 +5,15 @@
 #ifndef EXTENSIONS_RENDERER_API_BINDING_TYPES_H_
 #define EXTENSIONS_RENDERER_API_BINDING_TYPES_H_
 
+#include <memory>
+#include <vector>
+
 #include "base/callback.h"
 #include "v8/include/v8.h"
 
 namespace extensions {
+class ArgumentSpec;
+
 namespace binding {
 
 // A callback to execute the given v8::Function with the provided context and
@@ -18,6 +23,8 @@ using RunJSFunction = base::Callback<void(v8::Local<v8::Function>,
                                           int argc,
                                           v8::Local<v8::Value>[])>;
 
+using APISignature = std::vector<std::unique_ptr<ArgumentSpec>>;
+
 }  // namespace binding
 }  // namespace extensions