Allow arbitrary scale factors.

As discussed in https://codereview.chromium.org/1070433002/, this CL
allows arbitrary scale factors, which works because chromium uses the
resource most closely matching the scale factor (e.g. 1x for 1.25x,
but 2x for 1.9x) and scales it.

BUG=143619

Review URL: https://codereview.chromium.org/1078423002

Cr-Commit-Position: refs/heads/master@{#326851}

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

@@ -4,6 +4,7 @@
 
 #include "chrome/browser/ui/libgtk2ui/gtk2_ui.h"
 
+#include <math.h>
 #include <set>
 
 #include <pango/pango.h>
@@ -1427,8 +1428,9 @@ void Gtk2UI::UpdateDeviceScaleFactor(float device_scale_factor) {
 
 float Gtk2UI::GetDeviceScaleFactor() const {
   const int kCSSDefaultDPI = 96;
-  const float scale = GetDPI() / kCSSDefaultDPI;
-  return ui::GetScaleForScaleFactor(ui::GetSupportedScaleFactor(scale));
+  float scale = GetDPI() / kCSSDefaultDPI;
+  // Round to 2 decimals, e.g. to 1.33.
+  return roundf(scale * 100) / 100;
 }
 
 }  // namespace libgtk2ui

testing/xvfb.py

@@ -50,7 +50,7 @@ def start_xvfb(xvfb_path, display):
     xvfb_path: Path to Xvfb.
   """
   cmd = [xvfb_path, display, '-screen', '0', '1024x768x24', '-ac',
-         '-nolisten', 'tcp']
+         '-nolisten', 'tcp', '-dpi', '96']
   try:
     proc = subprocess.Popen(
         cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)