[lacros] Fix blurry Lacros window when display scale is fractional

This CL makes sure that LaCros windows receive big enough
wl_output.scale from exo when display scale is fractional by rounding it
up to the closest integer.

This is similar to how other compositors (Mutter, Sway) deal with
fractional scaling: clients are only aware of integer scaling and the
actual contents of windows are scaled down on the compositor side
(it's already done in Aura in our case).

Bug: 1093021
Change-Id: Ia47dd60dc0cb60396028c1ce108e095ecc84884f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2404930Reviewed-by: Mitsuru Oshima (Slow: gardener) <oshima@chromium.org>
Commit-Queue: Zakhar Voit <zvoit@igalia.com>
Cr-Commit-Position: refs/heads/master@{#806494}

components/exo/wayland/wayland_display_observer.cc

@@ -115,11 +115,10 @@ bool WaylandDisplayHandler::SendDisplayMetrics(const display::Display& display,
 
   if (wl_resource_get_version(output_resource_) >=
       WL_OUTPUT_SCALE_SINCE_VERSION) {
-    // Sending 100% if the scale is less then 100%, because wl_output_send_scale
-    // doesn't support fractional scale.
-    wl_output_send_scale(
-        output_resource_,
-        std::max(1, static_cast<int32_t>(display.device_scale_factor())));
+    // wl_output only supports integer scaling, so if device scale factor is
+    // fractional we need to round it up to the closest integer.
+    wl_output_send_scale(output_resource_,
+                         std::ceil(display.device_scale_factor()));
   }
 
   // TODO(reveman): Send real list of modes.