Remove Q_UNREACHABLE from DesktopScreenQt::GetDisplayNearestWindow

Chromium uses this method when the user attempts to drag.

Task-number: QTBUG-45723
Change-Id: Ibe3946846f0f4e2d2a25ca36e66fa7235d4aecea
Reviewed-by: Andras Becsi <andras.becsi@theqtcompany.com>

src/core/desktop_screen_qt.cpp

@@ -70,7 +70,8 @@ std::vector<gfx::Display> DesktopScreenQt::GetAllDisplays() const
 
 gfx::Display DesktopScreenQt::GetDisplayNearestWindow(gfx::NativeView window) const
 {
-    Q_UNREACHABLE();
+    // RenderViewHostImpl::OnStartDragging uses this to determine
+    // the scale factor for the view.
     return gfx::Display();
 }