ozone: scenic: Require mojo

This fixes a crash if you don't pass --enable-features=OzoneDrmMojo.
Oops.

Bug: 861853
Test: run_content_shell with no arguments
Change-Id: I5408ca9323b8481ed6c5f092172b75f2181c94fe
Reviewed-on: https://chromium-review.googlesource.com/c/1354502Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612002}

ui/ozone/platform/scenic/ozone_platform_scenic.cc

@@ -41,7 +41,7 @@ constexpr OzonePlatform::PlatformProperties kScenicPlatformProperties{
     /*needs_view_token=*/true,
     /*custom_frame_pref_default=*/false,
     /*use_system_title_bar=*/false,
-    /*requires_mojo=*/false};
+    /*requires_mojo=*/true};
 
 class ScenicPlatformEventSource : public ui::PlatformEventSource {
  public: