Fix Jumplist favicons to have high resolution in HDPI Windows displays

ui/display/win/screen_win.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 "ui/display/win/screen_win.h"
 
 #include <windows.h>
 #include <shellscalingapi.h>
 
 #include <algorithm>
@@ skipping 333 matching lines @@
   if (!g_screen_win_instance)
     return ScreenWinDisplay().display().device_scale_factor();
 
   DCHECK(hwnd);
   HWND rootHwnd = g_screen_win_instance->GetRootWindow(hwnd);
   ScreenWinDisplay screen_win_display =
       g_screen_win_instance->GetScreenWinDisplayNearestHWND(rootHwnd);
   return screen_win_display.display().device_scale_factor();
 }
 
+// static
+float ScreenWin::GetLargestDeviceScaleFactor() {

[sky, 2017/02/02 22:41:16]

This function is only needed in one place, can you move it there? The code
calling this can get all the displays and iterate over it there, right?

[chengx, 2017/02/03 01:51:13]

Sure. Will make the code local to jumplist.

+  float scale = 1.0;
+  if (!g_screen_win_instance)
+    return scale;
+  std::vector<Display> displays(g_screen_win_instance->GetAllDisplays());
+  for (size_t i = 0; i < displays.size(); i++) {

[sky, 2017/02/02 22:41:16]

no {}, also, I would use enhanced for loop

[chengx, 2017/02/03 01:51:13]

Done.

+    scale = std::max(scale, displays[i].device_scale_factor());
+  }
+  return scale;
+}
+
 HWND ScreenWin::GetHWNDFromNativeView(gfx::NativeView window) const {
   NOTREACHED();
   return nullptr;
 }
 
 gfx::NativeWindow ScreenWin::GetNativeWindowFromHWND(HWND hwnd) const {
   NOTREACHED();
   return nullptr;
 }
 
@@ skipping 223 matching lines @@
     if (std::find(unique_scale_factors.begin(), unique_scale_factors.end(),
                   reported_scale) == unique_scale_factors.end()) {
       unique_scale_factors.push_back(reported_scale);
       UMA_HISTOGRAM_SPARSE_SLOWLY("UI.DeviceScale", reported_scale);
     }
   }
 }
 
 }  // namespace win
 }  // namespace display