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

Source/wtf/MainThread.cpp

Index: Source/wtf/MainThread.cpp
diff --git a/Source/wtf/MainThread.cpp b/Source/wtf/MainThread.cpp
index 83a14aefb290aed59263a3af01fd5e6466dad94f..17b823e9eb24fd1ceb756dfccedaec791f1b501f 100644
--- a/Source/wtf/MainThread.cpp
+++ b/Source/wtf/MainThread.cpp
@@ -66,9 +66,9 @@ static void callFunctionObject(void* context)
     delete function;
 }
 
-void callOnMainThread(const Function<void()>& function)
+void callOnMainThread(PassOwnPtr<Function<void()>> function)
 {
-    callOnMainThread(callFunctionObject, new Function<void()>(function));
+    callOnMainThread(callFunctionObject, function.leakPtr());
 }
 
 bool isMainThread()