Make SVG stroke-dasharray animatable

Previously, SVG stroke-dasharray was not animatable; this change adds
the blendFunc and wires it up so that stroke dasharray is animatable.

This is a merge of a patch by rbuis in WebKit:
http://trac.webkit.org/changeset/153754

This patch differs from the WebKit patch by not using the c99 remainder() function. Consider the following fromLength and toLength values:
fromLength, toLength -> resultLength
1, 10 -> 10
10, 1 -> 10
2, 3 -> 6
3, 2 -> 6
If fromLength % toLength == 0, toLength divides fromLength evenly and we know fromLength is larger than toLength. This observation allows us to use mod instead of remainder(), max(), and min() calls.

BUG=269022

Review URL: https://chromiumcodereview.appspot.com/22494002

git-svn-id: svn://svn.chromium.org/blink/trunk@155714 bbb929c8-8fbe-4397-9dbb-9b2b20218538