This change takes all existing WebIDL files in the repo that had
definition lines without four leading spaces, and fixes them so they
have four leading spaces.
This represents the SVG <linearGradient>. The actual gradient is
converted to a Gfx::PaintStyle for use in SVG fills... There is a little
guesswork in the implementation, but it seems to match Chrome/Firefox.
Note: Still not hooked up to actual painting in this commit.
