X11 and Ozone: Fix screen initialization for Ozone config

The tests that use ClientHintsBrowserTest override FeatureList
during ::SetUp call, which results in erasing UseOzonePlatform
from that, and InProcessBrowserTest::SetScreenInstance cannot
check the status of the feature flag during ::SetUp call. And,
as a consequence, fail to decide what path it must use. Append
the UseOzonePlatform feature flag back to the scoped feature list
so that initialization happens properly.

-----

PS: Please note that this is a temp solution that will help to choose
between ozone and non-ozone X11 build. The switch that will be used
to choose the path is --enable-features=UseOzonePlatform. Once
non-Ozone X11 path is removed (hopefully by Q1 2021 depending on how
the finch trial goes), the wrapper will be removed.

Please also note that it's impossible to build use_x11 && use_ozone
without some hacks in PlatformCursor code. The changes to that are
on their way to upstream.

----

Bug: 1085700
Change-Id: I995a434a25b6e1a0db3d16bb516184c0d3bc87de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2333843Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Maksim Sisov (GMT+3) <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#796341}

chrome/browser/client_hints/client_hints_browsertest.cc

@@ -52,6 +52,7 @@
 #include "services/network/public/cpp/features.h"
 #include "services/network/public/cpp/network_switches.h"
 #include "third_party/blink/public/common/client_hints/client_hints.h"
+#include "ui/base/ui_base_features.h"
 
 namespace {
 
@@ -264,7 +265,23 @@ class ClientHintsBrowserTest : public policy::PolicyTest,
   }
 
   void SetUp() override {
-    scoped_feature_list_.InitWithFeatureList(EnabledFeatures());
+    auto enabled_features = EnabledFeatures();
+#if defined(USE_X11) && defined(USE_OZONE)
+    // The ClientHintsBrowserTest overrides features during SetUp call that
+    // results in UseOzonePlatform disabled (though, it was enabled in the
+    // beginning). Thus, make sure that we preserve this feature flag. PS:
+    // original feature list is restored right before BrowserMain and normal
+    // flow continues (UseOzonePlatform feature is there as well).
+    // TODO(https://crbug.com/1096425): remove this once USE_X11 goes away.
+    if (features::IsUsingOzonePlatform()) {
+      std::vector<base::FeatureList::FeatureOverrideInfo> overrides;
+      overrides.push_back(
+          {std::cref(features::kUseOzonePlatform),
+           base::FeatureList::OverrideState::OVERRIDE_ENABLE_FEATURE});
+      enabled_features->RegisterExtraFeatureOverrides(overrides);
+    }
+#endif
+    scoped_feature_list_.InitWithFeatureList(std::move(enabled_features));
     InProcessBrowserTest::SetUp();
   }
 

chrome/test/BUILD.gn

@@ -743,6 +743,7 @@ if (!is_android) {
       "//third_party/widevine/cdm:buildflags",
       "//third_party/widevine/cdm:headers",
       "//ui/accessibility:test_support",
+      "//ui/base:features",
       "//ui/base:test_support",
       "//ui/base/clipboard:clipboard_test_support",
       "//ui/base/dragdrop/mojom:mojom_shared",