Convert animation and renderer code to know about BorderImageLength

This propagates BorderImageLengthBox further out in the code, but
actually converts it to an actual number or length as soon as possible
in the animation code, and animates it as the individual type.

Now we can also remove the compatibility conversion methods between
BorderImageLengthBox and LengthBox.

Also, update a couple of "Weird number of spaces at line-start"
indentations in CSSPropertyAnimation.cpp to not make the new code
inconsistent with the old wrt. indentation.

BUG=259107

Review URL: https://codereview.chromium.org/55813002

git-svn-id: svn://svn.chromium.org/blink/trunk@161715 bbb929c8-8fbe-4397-9dbb-9b2b20218538
destroyLayer() should call setHasLayer(false)

This change synchronize clearing the layer and calling setHasLayer.
The old code would dissociate the 2 opeations to handle clean-ups
during RenderLayer::removeOnlyThisLayer. The dissociation was
introduced to handle https://bugs.webkit.org/show_bug.cgi?id=25252
and Eric wasn't sure at the time it was the right solution.

Based on the fact that the test is still passing, it wasn't.

Review URL: https://codereview.chromium.org/63693004

git-svn-id: svn://svn.chromium.org/blink/trunk@161716 bbb929c8-8fbe-4397-9dbb-9b2b20218538