[QT] Account for logical scale factor

Previously we were only using the device pixel ratio.  But QT UI
scales with both the device pixel ratio and the logical DPI.  This CL
sets Chrome's scale factor to be the product of these two.

R=thestig
CC=jkummerow

Change-Id: I9bd414046058e741450fabae4913d47a16ca48c3
Bug: 1439149
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4575572


Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1151380}