[Gin] Add a warning about potential memory leak for CreateFunctionTemplate

gin/function_template.h

 // Copyright 2014 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 GIN_FUNCTION_TEMPLATE_H_
 #define GIN_FUNCTION_TEMPLATE_H_
 
 #include "base/callback.h"
 #include "base/logging.h"
 #include "gin/arguments.h"
@@ skipping 202 matching lines @@
   }
 };
 
 }  // namespace internal
 
 
 // CreateFunctionTemplate creates a v8::FunctionTemplate that will create
 // JavaScript functions that execute a provided C++ function or base::Callback.
 // JavaScript arguments are automatically converted via gin::Converter, as is
 // the return value of the C++ function, if any.
+//
+// NOTE: V8 caches FunctionTemplates for a lifetime of a web page for its own
+// internal reasons, thus it is generally a good idea to cache the template
+// returned by this function.  Otherwise, repeated method invocations from JS
+// will create substantial memory leaks. See http://crbug.com/463487.
 template<typename Sig>
 v8::Local<v8::FunctionTemplate> CreateFunctionTemplate(
     v8::Isolate* isolate, const base::Callback<Sig> callback,
     int callback_flags = 0) {
   typedef internal::CallbackHolder<Sig> HolderT;
   HolderT* holder = new HolderT(isolate, callback, callback_flags);
 
   return v8::FunctionTemplate::New(
       isolate,
       &internal::Dispatcher<Sig>::DispatchToCallback,
@@ skipping 11 matching lines @@
   typedef internal::CallbackHolder<Sig> HolderT;
   HolderT* holder = new HolderT(isolate, callback, callback_flags);
   tmpl->SetCallAsFunctionHandler(&internal::Dispatcher<Sig>::DispatchToCallback,
                                  ConvertToV8<v8::Handle<v8::External> >(
                                      isolate, holder->GetHandle(isolate)));
 }
 
 }  // namespace gin
 
 #endif  // GIN_FUNCTION_TEMPLATE_H_