Allow playing video/webm on Windows

components/servo/lib.rs

@@ -166,6 +166,7 @@ mod media_platform {
         ];
 
         let non_uwp_plugins = [
+            "gstmatroska.dll",
             "gstnice.dll",
             "gstogg.dll",
             "gstopengl.dll",

python/servo/build_commands.py

@@ -892,6 +892,7 @@ def package_gstreamer_dlls(env, servo_exe_dir, target, uwp):
 
     if not uwp:
         gst_dlls += [
+            "gstmatroska.dll",
             "gstnice.dll",
             "gstogg.dll",
             "gstopengl.dll",