Neuter the "screen scale factor" computation for SVG <text>

This removes the PaintLayer-factor and DSF from the "screen scale factor",
leaving only the transform to the <svg> root and the "content transform" (used
by <pattern>, <mask> and <clipPath>.)

BUG=664961

Review-Url: https://codereview.chromium.org/2492013004
Cr-Commit-Position: refs/heads/master@{#435599}
3 files changed