Windows: cefclient: Improve high-dpi display (issue #1674).

- Add high-dpi support to the OSR example.
- Apply DPI scaling to the buttons and URL bar.

tests/cefclient/browser/root_window_win.h

@@ -112,6 +112,9 @@ class RootWindowWin : public RootWindow,
   // Draggable region.
   HRGN draggable_region_;
 
+  // Font for buttons and text fields.
+  HFONT font_;
+
   // Buttons.
   HWND back_hwnd_;
   HWND forward_hwnd_;