Revert "Remove GTK scale factor workarounds"

This reverts commit 2c2f5494.

Reason for revert: Potential culprit of bots failing in linux trusty rel, https://bugs.chromium.org/p/chromium/issues/detail?id=1065074

Original change's description:
> Remove GTK scale factor workarounds
> 
> The workarounds were initially added to fix rendering issues
> when the scale factor was an odd value like 1.01.  Hopefully
> the fractional scale factor support in Chrome is now good
> enough to handle these cases.
> 
> This change prevents unexpected scale factor behavior like
> 1.25 remapping to 1.0.
> 
> BUG=1033552
> R=​oshima
> 
> Change-Id: I1d22c1ddcf463fed12061ef265d2a6b4a4bcbeb8
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2121179
> Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
> Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#753653}

TBR=oshima@chromium.org,thomasanderson@chromium.org

Change-Id: I8094718a8ddc3b041fddfe194260d0503ce61d43
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1033552
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2122688Reviewed-by: Juanmi Huertas <juanmihd@chromium.org>
Commit-Queue: Juanmi Huertas <juanmihd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753763}

chrome/browser/ui/gtk/gtk_ui.cc

@@ -1096,7 +1096,12 @@ float GtkUi::GetRawDeviceScaleFactor() {
   gint scale = gtk_widget_get_scale_factor(fake_window_);
   DCHECK_GT(scale, 0);
   gdouble resolution = gdk_screen_get_resolution(screen);
-  return resolution <= 0 ? scale : resolution * scale / kDefaultDPI;
+  const float scale_factor =
+      resolution <= 0 ? scale : resolution * scale / kDefaultDPI;
+
+  // Blacklist scaling factors <120% (crbug.com/484400) and round
+  // to 1 decimal to prevent rendering problems (crbug.com/485183).
+  return scale_factor < 1.2f ? 1.0f : roundf(scale_factor * 10) / 10;
 }
 
 void GtkUi::UpdateDeviceScaleFactor() {