Animate clip rect() between different Length types
https://bugs.webkit.org/show_bug.cgi?id=115336

Reviewed by Andreas Kling.

Source/WebCore:

At the moment the animation for the 'clip' property
has an early return if the type of two Length values
does not match. This patch removes this early return.

Modified existing tests to cover the changes.

* page/animation/CSSPropertyAnimation.cpp:
(WebCore::blendFunc):

LayoutTests:

Modify test for clip animation to cover animations between
different Length types.

* transitions/clip-transition.html:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149288 268f45cc-cd09-0410-ab3c-d52691b4dbfc