Round the deviceScaleFactor for GTK

A previous change,
https://crrev.com/54668d23a68b82a35be7359cce9e4569e178cf6f,
removed rounding of the scale factor for GTK platforms.
This resulting in blurry content for some users with desktop
environments that give deviceScaleFactors of 1.002 and similar.

To address the problem, round the scale to 2 decimal places.

Fixed: 1087109
Change-Id: I17364d69facc3745528a8971bb2616ff76eb9b25
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2639816Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845887}

ui/gtk/gtk_ui.cc

@@ -1073,14 +1073,13 @@ float GtkUi::GetRawDeviceScaleFactor() {
   DCHECK_GT(scale, 0.0);
 
   gdouble resolution = gdk_screen_get_resolution(screen);
-  // TODO(https://crbug.com/1033552): Remove this hack once the Trusty bots are
-  // fixed to have a resolution of 96, or when the Trusty bots are removed
-  // altogether.
-  if (std::abs(resolution - 95.8486) < 0.001)
-    resolution = 96;
   if (resolution > 0)
     scale *= resolution / kDefaultDPI;
 
+  // Round to 2 decimal places to address problems with some Linux desktop
+  // environments that result in scales of 1.002... and the like.
+  scale = roundf(scale * 100.0) / 100;
+
   return scale;
 }