Hookup device dpi for ChromeOS

chrome/browser/extensions/display_info_provider_chromeos.cc

Index: chrome/browser/extensions/display_info_provider_chromeos.cc
diff --git a/chrome/browser/extensions/display_info_provider_chromeos.cc b/chrome/browser/extensions/display_info_provider_chromeos.cc
index fcb87ed100589fb4f622cdef7df8b3a68f3625db..6abeac5ecbf2fd997647ace03291137c037323d3 100644
--- a/chrome/browser/extensions/display_info_provider_chromeos.cc
+++ b/chrome/browser/extensions/display_info_provider_chromeos.cc
@@ -366,10 +366,9 @@ void DisplayInfoProviderChromeOS::UpdateDisplayUnitInfoForPlatform(
         base::Int64ToString(display_manager->mirroring_display_id());
   }
 
-  // TODO(hshi): determine the DPI of the screen.
-  const float kDpi96 = 96.0;
-
-  const float dpi = display.device_scale_factor() * kDpi96;
+  const ash::DisplayInfo& display_info = display_manager->GetDisplayInfo(
+      display.id());
+  const float dpi = display_info.device_dpi() / display.device_scale_factor();
   unit->dpi_x = dpi;
   unit->dpi_y = dpi;