Enable hidpi on Linux, refactor a bit on Windows to share

ui/views/widget/desktop_aura/desktop_screen_x11.cc

Index: ui/views/widget/desktop_aura/desktop_screen_x11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_screen_x11.cc b/ui/views/widget/desktop_aura/desktop_screen_x11.cc
index bb253cff17ce48e6295bbee89574a874f5733462..d5b1f52da25e4b850ea9dfe1c76420325fe15eec 100644
--- a/ui/views/widget/desktop_aura/desktop_screen_x11.cc
+++ b/ui/views/widget/desktop_aura/desktop_screen_x11.cc
@@ -20,6 +20,7 @@
 #include "ui/display/util/x11/edid_parser_x11.h"
 #include "ui/events/platform/platform_event_source.h"
 #include "ui/gfx/display.h"
+#include "ui/gfx/dpi.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/screen.h"
 #include "ui/gfx/x/x11_types.h"
@@ -33,18 +34,6 @@ namespace {
 // in |Dispatch()|.
 const int64 kConfigureDelayMs = 500;
 
-// TODO(oshima): Consider using gtk-xft-dpi instead.
-float GetDeviceScaleFactor(int screen_pixels, int screen_mm) {
-  const int kCSSDefaultDPI = 96;
-  const float kInchInMm = 25.4f;
-
-  float screen_inches = screen_mm / kInchInMm;
-  float screen_dpi = screen_pixels / screen_inches;
-  float scale = screen_dpi / kCSSDefaultDPI;
-
-  return ui::GetScaleForScaleFactor(ui::GetSupportedScaleFactor(scale));
-}
-
 std::vector<gfx::Display> GetFallbackDisplayList() {
   ::XDisplay* display = gfx::GetXDisplay();
   ::Screen* screen = DefaultScreenOfDisplay(display);
@@ -56,8 +45,7 @@ std::vector<gfx::Display> GetFallbackDisplayList() {
   gfx::Display gfx_display(0, bounds_in_pixels);
   if (!gfx::Display::HasForceDeviceScaleFactor() &&
       !ui::IsDisplaySizeBlackListed(physical_size)) {
-    float device_scale_factor = GetDeviceScaleFactor(
-        width, physical_size.width());
+    float device_scale_factor = gfx::GetDeviceScaleFactor();
     DCHECK_LE(1.0f, device_scale_factor);
     gfx_display.SetScaleAndBounds(device_scale_factor, bounds_in_pixels);
   }
@@ -279,7 +267,7 @@ std::vector<gfx::Display> DesktopScreenX11::BuildDisplaysFromXRandRInfo() {
     has_work_area = true;
   }
 
-  float device_scale_factor = 1.0f;
+  float device_scale_factor = gfx::GetDeviceScaleFactor();
   for (int i = 0; i < resources->noutput; ++i) {
     RROutput output_id = resources->outputs[i];
     XRROutputInfo* output_info =
@@ -306,17 +294,8 @@ std::vector<gfx::Display> DesktopScreenX11::BuildDisplaysFromXRandRInfo() {
       gfx::Rect crtc_bounds(crtc->x, crtc->y, crtc->width, crtc->height);
       gfx::Display display(display_id, crtc_bounds);
 
-      if (!gfx::Display::HasForceDeviceScaleFactor()) {
-        if (i == 0 && !ui::IsDisplaySizeBlackListed(
-            gfx::Size(output_info->mm_width, output_info->mm_height))) {
-          // As per display scale factor is not supported right now,
-          // the primary display's scale factor is always used.
-          device_scale_factor = GetDeviceScaleFactor(crtc->width,
-                                                     output_info->mm_width);
-          DCHECK_LE(1.0f, device_scale_factor);
-        }
+      if (!gfx::Display::HasForceDeviceScaleFactor())
         display.SetScaleAndBounds(device_scale_factor, crtc_bounds);
-      }
 
       if (has_work_area) {
         gfx::Rect intersection = crtc_bounds;