Remove [Affine|Transformation]Matrix dependency on SkMatrix

Remove SkMatrix operator from AffineTransform and TransformationMatrix
thereby breaking the dependency on SkMatrix and Skia.

Instead add explicit conversion function to SkiaUtils and update the
handful of call sites to use the explicit function instead of the
implicit operator.

BUG=303225
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/25478013

git-svn-id: svn://svn.chromium.org/blink/trunk@158764 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move Supplementable from core/platform to platform.

BUG=297477
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/25799002

git-svn-id: svn://svn.chromium.org/blink/trunk@158765 bbb929c8-8fbe-4397-9dbb-9b2b20218538