ozone/linux: allow native events to be sent in ui tests.

When Ozone/X11 starts to use emulated ui events, it's required that
X11Window is able to send out those events further to aura.

Thus, restrict this limit only to ChromeOS as it uses different approach
for ui tests (it basically sends events using UiControlsAsh).

Bug: 1134495
Change-Id: Ifa4d143b178be0e49449cfd843981a375d71a74b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2444310Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Maksim Sisov (GMT+3) <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#814333}

ui/aura/test/aura_test_helper.cc

@@ -63,7 +63,7 @@ AuraTestHelper::AuraTestHelper(ui::ContextFactory* context_factory,
   ui::test::EnableTestConfigForPlatformWindows();
 #endif
 
-#if defined(USE_OZONE)
+#if defined(USE_OZONE) && defined(OS_CHROMEOS)
   ui::DisableNativeUiEventDispatchForTest();
 #endif