Update from https://crrev.com/302630

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 132 matching lines @@
 
 template <size_t... indices, typename... ArgTypes>
 class Invoker<IndicesHolder<indices...>, ArgTypes...>
     : public ArgumentHolder<indices, ArgTypes>... {
  public:
   // Invoker<> inherits from ArgumentHolder<> for each argument.
   // C++ has always been strict about the class initialization order,
   // so it is guaranteed ArgumentHolders will be initialized (and thus, will
   // extract arguments from Arguments) in the right order.
   Invoker(Arguments* args, int create_flags)
-      : ArgumentHolder<indices, ArgTypes>(args, create_flags)...,
-        args_(args) {}
+      : ArgumentHolder<indices, ArgTypes>(args, create_flags)..., args_(args) {
+    // GCC thinks that create_flags is going unused, even though the
+    // expansion above clearly makes use of it. Per jyasskin@, casting
+    // to void is the commonly accepted way to convince the compiler
+    // that you're actually using a parameter/varible.
+    (void)create_flags;
+  }
 
   bool IsOK() {
     return And(ArgumentHolder<indices, ArgTypes>::ok...);
   }
 
   template <typename ReturnType>
   void DispatchToCallback(base::Callback<ReturnType(ArgTypes...)> callback) {
     args_->Return(callback.Run(ArgumentHolder<indices, ArgTypes>::value...));
   }
 
@@ skipping 70 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_