Prevent crash when track is deleted during video element deletion.
https://bugs.webkit.org/show_bug.cgi?id=106183

Reviewed by Dean Jackson.

Source/WebCore:

Test: media/track/track-remove-crash.html

* html/HTMLMediaElement.cpp:
(WebCore::HTMLMediaElement::removedFrom): Set m_inActiveDocument to false so we
    do not process text track cues or dispatch related events.

LayoutTests:

* media/track/track-remove-crash-expected.txt: Added.
* media/track/track-remove-crash.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149749 268f45cc-cd09-0410-ab3c-d52691b4dbfc