Fix Linux ozone build

BUG=None
R=sky
CC=​tonikitoo@igalia.com,msisov@igalia.com
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_chromium_ozone_compile_only_ng

Change-Id: I2f2768169a029b76e51aff1d3a695d84b8edcabf
Reviewed-on: https://chromium-review.googlesource.com/881951Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531389}

content/shell/browser/shell_views.cc

@@ -347,7 +347,9 @@ void Shell::PlatformInitialize(const gfx::Size& default_window_size) {
 #if defined(USE_AURA)
   wm_state_ = new wm::WMState;
 #endif
+#if !defined(USE_OZONE)
   display::Screen::SetScreenInstance(views::CreateDesktopScreen());
+#endif
 #endif
   views_delegate_ = new views::DesktopTestViewsDelegate();
 }