Move createClosure from V8PromiseCustom.cpp to V8Binding.h

Source/bindings/v8/custom/V8PromiseCustom.cpp

Index: Source/bindings/v8/custom/V8PromiseCustom.cpp
diff --git a/Source/bindings/v8/custom/V8PromiseCustom.cpp b/Source/bindings/v8/custom/V8PromiseCustom.cpp
index d0a968336057279b07fab8642aa7d911e27bffe9..8253f04b3d5df537f84ec4ea5f289c563a7d7958 100644
--- a/Source/bindings/v8/custom/V8PromiseCustom.cpp
+++ b/Source/bindings/v8/custom/V8PromiseCustom.cpp
@@ -51,11 +51,6 @@ namespace WebCore {
 
 namespace {
 
-v8::Local<v8::Function> createClosure(v8::FunctionCallback function, v8::Handle<v8::Value> environment)
-{
-    return v8::FunctionTemplate::New(function, environment)->GetFunction();
-}
-
 class PromiseTask : public ScriptExecutionContext::Task {
 public:
     PromiseTask(v8::Handle<v8::Function> callback, v8::Handle<v8::Object> receiver, v8::Handle<v8::Value> result)