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

Source/wtf/MainThread.cpp

 /*
 * Copyright (C) 2009 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
@@ skipping 48 matching lines @@
     (*callOnMainThreadFunction)(function, context);
 }
 
 static void callFunctionObject(void* context)
 {
     Function<void()>* function = static_cast<Function<void()>*>(context);
     (*function)();
     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()
 {
     return currentThread() == mainThreadIdentifier;
 }
 
 } // namespace WTF