servo: Merge #6232 - DRY submodule updating by utilizing existing update-submodules command (from frewsxcv:update-submodules-dry); r=jdm

This might allow us to merge #5648

Source-Repo: https://github.com/servo/servo
Source-Revision: 1d19338a93348c4e817a0b1619dc236881ba18f6

servo/python/servo/command_base.py

@@ -224,15 +224,7 @@ class CommandBase(object):
         if self.context.bootstrapped:
             return
 
-        subprocess.check_call(["git", "submodule", "--quiet", "sync", "--recursive"])
-        submodules = subprocess.check_output(["git", "submodule", "status"])
-        for line in submodules.split('\n'):
-            components = line.strip().split(' ')
-            if len(components) > 1 and components[0].startswith(('-', '+')):
-                module_path = components[1]
-                subprocess.check_call(["git", "submodule", "update",
-                                       "--init", "--recursive",
-                                       "--", module_path])
+        Registrar.dispatch("update-submodules", context=self.context)
 
         if not self.config["tools"]["system-rust"] and \
            not path.exists(path.join(