DevTools: fix screenshot clipping on retina displays

Currently, computation of screenshot dimensions has a rounding error
that surfaces on retina displays.

This patch starts rounding screenshot dimensions up and then truncating
them if necesseary.

Bug: chromium:763657
Change-Id: I8953c32af76d216893fb43a62eaa440a15e2652a
Reviewed-on: https://chromium-review.googlesource.com/726746
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510285}
2 files changed