Allow Chrome's Non-Client Area To Be Scaled on DPI Changes

ui/gfx/win/window_impl.cc

Index: ui/gfx/win/window_impl.cc
diff --git a/ui/gfx/win/window_impl.cc b/ui/gfx/win/window_impl.cc
index bf43ba59045490bbb0c169dcfe12637745d6fb36..a7077c478c5444962a971b6b9f0390da112538ef 100644
--- a/ui/gfx/win/window_impl.cc
+++ b/ui/gfx/win/window_impl.cc
@@ -12,6 +12,7 @@
 #include "base/memory/singleton.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/synchronization/lock.h"
+#include "base/win/win_util.h"
 #include "base/win/wrapped_window_proc.h"
 #include "ui/gfx/win/hwnd_util.h"
 
@@ -212,6 +213,22 @@ void WindowImpl::Init(HWND parent, const Rect& bounds) {
                              reinterpret_cast<wchar_t*>(atom), NULL,
                              window_style_, x, y, width, height,
                              parent, NULL, NULL, this);
+  if (hwnd && base::win::IsProcessPerMonitorDpiAware()) {
+    static auto enable_child_window_dpi_message_func = []() {
+      // Derived signature; not available in headers.
+      // This call gets Windows to scale the non-client area when WM_DPICHANGED
+      // is fired.

[scottmg, 2016/06/27 19:26:35]

Any semi-documentation you can link here?

[robliao, 2016/06/27 19:58:07]

Unfortunately not that I can find. This is pretty leading edge.

+      using EnableChildWindowDpiMessagePtr = LRESULT (WINAPI*)(HWND, BOOL);
+      HMODULE user32 = GetModuleHandle(L"user32");

[scottmg, 2016/06/27 19:26:35]

Other instances seem to include ".dll".

[robliao, 2016/06/27 19:58:07]

Done.

+      if (user32) {

[scottmg, 2016/06/27 19:26:35]

Don't think you need to check user32 here, just inline into GetProcAddress(); we
just called CreateWindowEx() above.

[robliao, 2016/06/27 19:58:07]

Done. Yup, we seem to do it in other places indeed. Just wanted to guard against
other faliures that GetModuleHandle would encounter, but then we would be in
trouble in other places anyways.

+        return reinterpret_cast<EnableChildWindowDpiMessagePtr>(
+                   GetProcAddress(user32, "EnableChildWindowDpiMessage"));
+      }
+      return reinterpret_cast<EnableChildWindowDpiMessagePtr>(nullptr);
+    }();
+    if (enable_child_window_dpi_message_func)
+      enable_child_window_dpi_message_func(hwnd, TRUE);
+  }
 
   // First nccalcszie (during CreateWindow) for captioned windows is
   // deliberately ignored so force a second one here to get the right