PingLoader objects unnecessarily pass through OwnPtr

PingLoader objects unnecessarily pass through OwnPtr
https://bugs.webkit.org/show_bug.cgi?id=122942

Reviewed by Darin Adler.

There's no need to store new PingLoader objects into an OwnPtr just to leak them out a few lines later
into an unused variable. New objects are created through a new helper method and then left unmanaged as
they're guaranteed to destroy themselves when they receive a response of any kind.

* loader/PingLoader.cpp:
(WebCore::PingLoader::loadImage): Call the new createPingLoader method to spawn the PingLoader.
(WebCore::PingLoader::sendPing): Ditto.
(WebCore::PingLoader::sendViolationReport): Ditto.
(WebCore::PingLoader::createPingLoader): A helper method that creates a new PingLoader object
* loader/PingLoader.h: Declare the new PingLoader::createPingLoader method.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@158558 268f45cc-cd09-0410-ab3c-d52691b4dbfc