[GStreamer] audio is muted when playback rate is between 0.8 and 2.0
https://bugs.webkit.org/show_bug.cgi?id=109362

Reviewed by Martin Robinson.

Don't mute sound if the audio pitch is preserved. If this is not
the case mute it if it's too extreme, as the HTML5 spec recommends.

* platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.cpp:
(WebCore::MediaPlayerPrivateGStreamer::setRate):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142391 268f45cc-cd09-0410-ab3c-d52691b4dbfc