Add PlatformWindow/Event related code for Ozone X11.

media/ozone/media_ozone_platform.cc

Index: media/ozone/media_ozone_platform.cc
diff --git a/media/ozone/media_ozone_platform.cc b/media/ozone/media_ozone_platform.cc
index c1c45864c28d67bf6034f2ded078ff6deb05b28e..417d54c0e3d07d95f0151251382d8f7734df3f65 100644
--- a/media/ozone/media_ozone_platform.cc
+++ b/media/ozone/media_ozone_platform.cc
@@ -61,6 +61,10 @@ MediaOzonePlatform* CreateMediaOzonePlatformWayland() {
   return new MediaOzonePlatformStub;
 }
 
+MediaOzonePlatform* CreateMediaOzonePlatformX11() {
+  return new MediaOzonePlatformStub;
+}
+
 MediaOzonePlatform::MediaOzonePlatform() {
   CHECK(!instance_) << "There should only be a single MediaOzonePlatform.";
   instance_ = this;