[Extensions Bindings] Make function definitions optional for an API.

extensions/renderer/api_binding.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_BINDING_H_
 #define EXTENSIONS_RENDERER_API_BINDING_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 39 matching lines @@
                           v8::Local<v8::Function>)>;
 
   // The callback for determining if a given API method (specified by |name|)
   // is available.
   using AvailabilityCallback = base::Callback<bool(const std::string& name)>;
 
   // The callback type for handling an API call.
   using HandlerCallback = base::Callback<void(gin::Arguments*)>;
 
   // The ArgumentSpec::RefMap is required to outlive this object.
-  // |type_definitions| and |event_definitions| may be null if the API does not
-  // specify any types or events.
+  // |function_definitions|, |type_definitions| and |event_definitions|
+  // may be null if the API does not specify any of that category.
   APIBinding(const std::string& name,
-             const base::ListValue& function_definitions,
+             const base::ListValue* function_definitions,
              const base::ListValue* type_definitions,
              const base::ListValue* event_definitions,
              const APIMethodCallback& callback,
              std::unique_ptr<APIBindingHooks> binding_hooks,
              ArgumentSpec::RefMap* type_refs);
   ~APIBinding();
 
   // Returns a new v8::Object for the API this APIBinding represents.
   v8::Local<v8::Object> CreateInstance(
       v8::Local<v8::Context> context,
@@ skipping 31 matching lines @@
   const ArgumentSpec::RefMap* type_refs_;
 
   base::WeakPtrFactory<APIBinding> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(APIBinding);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_API_BINDING_H_