device scale factor detection: use gtk-xft-dpi consistently
Before this CL, we used either gtk-xft-dpi (UI fonts) or the physical DPI of
a more or less random display. This CL consistently uses gtk-xft-dpi which
is the better alternative: users can directly influence it (by changing the
Xft.dpi X resource, or via their gtkrc).
See also https://github.com/derat/font-config-info for displaying your
current system settings.
BUG=473089,143619
Review URL: https://codereview.chromium.org/1070433002
Cr-Commit-Position: refs/heads/master@{#324782}
4 files changed
