Keep using the same DPI scale

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/libgtk2ui/gtk2_ui.h"
 
 #include <math.h>
 #include <pango/pango.h>
 #include <set>
 #include <utility>
@@ skipping 413 matching lines @@
     params.subpixel_rendering = gfx::FontRenderParams::SUBPIXEL_RENDERING_NONE;
   }
 
   g_free(hint_style);
   g_free(rgba);
 
   return params;
 }
 
 double GetDPI() {
-  GtkSettings* gtk_settings = gtk_settings_get_default();
-  CHECK(gtk_settings);
-  gint gtk_dpi = -1;
-  g_object_get(gtk_settings, "gtk-xft-dpi", &gtk_dpi, NULL);
+  // Linux chrome currently does not support dynamic DPI changes.
+  // Keep using the first value detected.

[Elliot Glaysher, 2016/06/01 17:22:43]

I has a sad.

+  static double dpi = -1.f;
+  if (dpi < 0) {
+    const double kDefaultDPI = 96;
 
-  // GTK multiplies the DPI by 1024 before storing it.
-  return (gtk_dpi > 0) ? gtk_dpi / 1024.0 : 96.0;
+    GtkSettings* gtk_settings = gtk_settings_get_default();
+    CHECK(gtk_settings);
+    gint gtk_dpi = -1;
+    g_object_get(gtk_settings, "gtk-xft-dpi", &gtk_dpi, NULL);
+
+    // GTK multiplies the DPI by 1024 before storing it.
+    dpi = (gtk_dpi > 0) ? gtk_dpi / 1024.0 : kDefaultDPI;
+
+    // DSF is always >=1.0 on win/cros and lower DSF has never been considered
+    // nor tested.
+    dpi = std::max(kDefaultDPI, dpi);
+  }
+  return dpi;
 }
 
 // Queries GTK for its font DPI setting and returns the number of pixels in a
 // point.
 double GetPixelsInPoint(float device_scale_factor) {
   double dpi = GetDPI();
 
   // Take device_scale_factor into account — if Chrome already scales the
   // entire UI up by 2x, we should not also scale up.
   dpi /= device_scale_factor;
@@ skipping 938 matching lines @@
   // Blacklist scaling factors <130% (crbug.com/484400) and round
   // to 1 decimal to prevent rendering problems (crbug.com/485183).
   return scale < 1.3f ? 1.0f : roundf(scale * 10) / 10;
 }
 
 }  // namespace libgtk2ui
 
 views::LinuxUI* BuildGtk2UI() {
   return new libgtk2ui::Gtk2UI;
 }