Compute the base dpi from X

X uses 96 as default, and alters the screen size
but it can be overwritten. Compute the dpi from X
to match what gtk sues as base.

Round the dsf to 1 decimals as finer grained value can cause rendering problem than benefit.

Gpu test expectation on nvidia needs to be updated, so mark these tests as failing now.

BUG=485183,498426

Review URL: https://codereview.chromium.org/1136913005

Cr-Commit-Position: refs/heads/master@{#330212}
(cherry picked from commit 5cb0c01e4233ff3eb1e7f6f677b4cf9dae9ffaf2)

R=laforge@chromium.org
TBR=laforge@chromium.org, oshima@chromium.org

Review URL: https://codereview.chromium.org/1174483003.

Cr-Commit-Position: refs/branch-heads/2357@{#470}
Cr-Branched-From: 59d4494849b405682265ed5d3f5164573b9a939b-refs/heads/master@{#323860}
3 files changed