Fix setCurrentTime for paused animations

Fix setCurrentTime for paused animations
https://bugs.webkit.org/show_bug.cgi?id=81350

Reviewed by Nikolas Zimmermann.

Source/WebCore:

SMILTimeContainer::setElapsed was not resetting the pause time, breaking
setCurrentTime if the animation was paused.

Test: svg/custom/animate-pause-resume.html

* svg/animation/SMILTimeContainer.cpp:
(WebCore::SMILTimeContainer::setElapsed):

LayoutTests:

This test does not use the SVG animation test framework because the framework
works by pausing animations and testing animated values at fixed times
(through calling setCurrentTime). Testing this patch requires that we run
the animation and cannot be tested with the animation test framework.

* svg/custom/animate-pause-resume-expected.txt: Added.
* svg/custom/animate-pause-resume.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121246 268f45cc-cd09-0410-ab3c-d52691b4dbfc