Make 'transform' a presentation attribute on SVG elements

This makes 'transform', 'gradientTransform' and 'patternTransform'
presentation attributes on SVGGraphicsElements, SVGGradientElements
and SVGPatternElements respectively.

Spec:

 http://www.w3.org/TR/css3-transforms/#svg-transform
 http://www.w3.org/TR/css3-transforms/#svg-syntax
 http://www.w3.org/TR/css3-transforms/#svg-gradient-transform-pattern-transform

Salvaged from https://codereview.chromium.org/423093014, but takes a
different approach to bridge the syntax gap and avoid crbug.com/577219.

The strategy taken here is to use the SVGTransformList to generate a
CSSValue for the presentation attribute style, and hence postponing
both support for the full transform syntax and a way around the bug
mentioned above. Essentially softening the blow. These two "features"
are expected to be implemented eventually, so this is just a "first
step".

BUG=369942
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2478233002
Cr-Commit-Position: refs/heads/master@{#434934}
63 files changed