Bug 1824943 [VAAPI] Don't init VAAPI in child process r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D173950

gfx/thebes/gfxPlatformGtk.cpp

@@ -227,6 +227,10 @@ void gfxPlatformGtk::InitDmabufConfig() {
 bool gfxPlatformGtk::InitVAAPIConfig(bool aForceEnabledByUser) {
   FeatureState& feature =
       gfxConfig::GetFeature(Feature::HARDWARE_VIDEO_DECODING);
+  // We're already configured in parent process
+  if (!XRE_IsParentProcess()) {
+    return feature.IsEnabled();
+  }
 #ifdef MOZ_WAYLAND
   feature.EnableByDefault();