events: ozone: Prefer addition to subtraction in GN

In GYP we used to add all sources and then remove the unneeded ones.
Switch to addition which requires only listing the sources in one place.

Bug: 1026406

Change-Id: Ib085e35b59d3141e85b3265a0e849092adb9d1d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1943369Reviewed-by: Kevin Schoedel <kpschoedel@chromium.org>
Commit-Queue: Michael Spang <spang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720294}

ui/events/ozone/BUILD.gn

@@ -20,8 +20,6 @@ component("ozone") {
     "device/device_manager.h",
     "device/device_manager_manual.cc",
     "device/device_manager_manual.h",
-    "device/udev/device_manager_udev.cc",
-    "device/udev/device_manager_udev.h",
     "features.cc",
     "features.h",
     "gamepad/gamepad_event.cc",
@@ -44,14 +42,11 @@ component("ozone") {
 
   defines = [ "IS_EVENTS_OZONE_IMPL" ]
 
-  if (!use_udev) {
-    sources -= [
+  if (use_udev) {
+    sources += [
       "device/udev/device_manager_udev.cc",
       "device/udev/device_manager_udev.h",
     ]
-  }
-
-  if (use_udev) {
     deps += [ "//device/udev_linux" ]
   }
 }