HTMLMediaPlayer should free m_player when src is set/changed

HTMLMediaPlayer should free m_player when src is set/changed
https://bugs.webkit.org/show_bug.cgi?id=99647

Reviewed by Eric Carlson.

.:

* ManualTests/media-players-are-dropped-on-error.html: Added.
    Various scenarios are tested to make sure players aren't
    leaked in different ways for each of them.

Source/WebCore:

New ManualTest added; manual since leaking media players doesn't have layoutTestController-visible effects.

* html/HTMLMediaElement.cpp:
(WebCore::HTMLMediaElement::parseAttribute): clearMediaPlayer() when src is set/changed
(WebCore::HTMLMediaElement::userCancelledLoad): use new clearMediaPlayer() helper
(WebCore::HTMLMediaElement::clearMediaPlayer): clear m_player and associated timers/flags
(WebCore):
(WebCore::HTMLMediaElement::createMediaPlayer): whitespace-only change
* html/HTMLMediaElement.h: new method: createMediaPlayer().
(HTMLMediaElement):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@133252 268f45cc-cd09-0410-ab3c-d52691b4dbfc