X11 and Ozone: fix use_x11 && use_x11 build for desktop_screen

When use_x11 && use_ozone are set to true at the same
time, compiler throws an error about multiple definitions
of the CreateDesktopScreen.

Thus, to fix that, create a separate source file for
is_linux case that will choose what DesktopScreen to
use based on the IsUsingOzonePlatform feature flag.

Please note that this is a temp solution and it will
be removed once use_x11 goes away.

Please 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: I8710809572cc82d514ee64af1fe9a6a1eff73cd9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2247719Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#779213}

ui/views/BUILD.gn

@@ -784,7 +784,8 @@ jumbo_component("views") {
           "widget/desktop_aura/desktop_window_tree_host_win.cc",
         ]
         deps += [ "//ui/events:dom_keyboard_layout" ]
-      } else if (use_ozone) {
+      }
+      if (use_ozone) {
         public += [ "widget/desktop_aura/desktop_screen_ozone.h" ]
         sources += [
           "widget/desktop_aura/desktop_drag_drop_client_ozone.cc",
@@ -796,6 +797,7 @@ jumbo_component("views") {
         public += [ "widget/desktop_aura/desktop_window_tree_host_linux.h" ]
         sources += [
           "style/platform_style_linux.cc",
+          "widget/desktop_aura/desktop_screen_linux.cc",
           "widget/desktop_aura/desktop_window_tree_host_linux.cc",
           "widget/desktop_aura/window_event_filter_linux.cc",
           "widget/desktop_aura/window_event_filter_linux.h",

ui/views/widget/desktop_aura/desktop_screen_linux.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/views/widget/desktop_aura/desktop_screen.h"
+
+#if defined(USE_X11)
+#include "ui/views/widget/desktop_aura/desktop_screen_x11.h"
+#endif
+
+#if defined(USE_OZONE)
+#include "ui/base/ui_base_features.h"
+#include "ui/views/widget/desktop_aura/desktop_screen_ozone.h"
+#endif
+
+namespace views {
+
+display::Screen* CreateDesktopScreen() {
+#if defined(USE_OZONE)
+  if (features::IsUsingOzonePlatform())
+    return new DesktopScreenOzone();
+#endif
+#if defined(USE_X11)
+  auto* screen = new DesktopScreenX11();
+  screen->Init();
+  return screen;
+#else
+  NOTREACHED();
+  return nullptr;
+#endif
+}
+
+}  // namespace views

ui/views/widget/desktop_aura/desktop_screen_ozone.cc

@@ -4,6 +4,7 @@
 
 #include "ui/views/widget/desktop_aura/desktop_screen_ozone.h"
 
+#include "build/build_config.h"
 #include "ui/aura/screen_ozone.h"
 #include "ui/views/widget/desktop_aura/desktop_screen.h"
 #include "ui/views/widget/desktop_aura/desktop_window_tree_host_platform.h"
@@ -22,8 +23,13 @@ gfx::NativeWindow DesktopScreenOzone::GetNativeWindowFromAcceleratedWidget(
       widget);
 }
 
+// To avoid multiple definitions when use_x11 && use_ozone is true, disable this
+// factory method for OS_LINUX as Linux has a factory method that decides what
+// screen to use based on IsUsingOzonePlatform feature flag.
+#if !defined(OS_LINUX)
 display::Screen* CreateDesktopScreen() {
   return new DesktopScreenOzone();
 }
+#endif
 
 }  // namespace views

ui/views/widget/desktop_aura/desktop_screen_x11.cc

@@ -178,12 +178,4 @@ float DesktopScreenX11::GetXDisplayScaleFactor() const {
              : 1.0f;
 }
 
-////////////////////////////////////////////////////////////////////////////////
-
-display::Screen* CreateDesktopScreen() {
-  auto* screen = new DesktopScreenX11;
-  screen->Init();
-  return screen;
-}
-
 }  // namespace views