Rename transformToRoot:ish names to screenScaleFactorChanged:ish ones

This better reflects the function of this machinery, since it's used to
update the scale of fonts based on the computed "screen scale factor".

BUG=603956

Review URL: https://codereview.chromium.org/1911473002

Cr-Commit-Position: refs/heads/master@{#388749}
6 files changed