Change the return type of WTF::bind() to |OwnPtr<Function>|

Source/core/dom/Microtask.cpp

Index: Source/core/dom/Microtask.cpp
diff --git a/Source/core/dom/Microtask.cpp b/Source/core/dom/Microtask.cpp
index 56de67277d06b9b141435a0f1769d19bbdb97e19..42a5c065eacb6abd65d9cc7ab1fe968bd80f780f 100644
--- a/Source/core/dom/Microtask.cpp
+++ b/Source/core/dom/Microtask.cpp
@@ -73,7 +73,7 @@ void Microtask::enqueueMicrotask(PassOwnPtr<WebThread::Task> callback)
     isolate->EnqueueMicrotask(&microtaskFunctionCallback, callback.leakPtr());
 }
 
-void Microtask::enqueueMicrotask(const Closure& callback)
+void Microtask::enqueueMicrotask(PassOwnPtr<Closure> callback)
 {
     enqueueMicrotask(adoptPtr(new Task(callback)));
 }