Bug 1901912 - Restore the XPCOM registration of MessengerProfileMigrator. r=mkmelin

Differential Revision: https://phabricator.services.mozilla.com/D213365

--HG--
extra : rebase_source : c3c6b951f743e0da78544911f0ff1d646a363d5b
extra : amend_source : 8290782e432a5f3a6a8b429936f5d99de4dbead1

mail/components/components.conf

@@ -21,13 +21,13 @@ Classes = [
             "@mozilla.org/network/protocol/about;1?what=import",
             "@mozilla.org/network/protocol/about;1?what=profiling",
         ],
-        'esModule': "resource:///modules/AboutRedirector.sys.mjs",
+        "esModule": "resource:///modules/AboutRedirector.sys.mjs",
         "constructor": "AboutRedirector",
     },
     {
         "cid": "{eb239c82-fac9-431e-98d7-11cacd0f71b8}",
         "contract_ids": ["@mozilla.org/mail/mailglue;1"],
-        'esModule': "resource:///modules/MailGlue.sys.mjs",
+        "esModule": "resource:///modules/MailGlue.sys.mjs",
         "constructor": "MailGlue",
     },
     {
@@ -53,6 +53,12 @@ Classes = [
         "esModule": "resource:///modules/MessengerContentHandler.sys.mjs",
         "constructor": "MessageDisplayContentHandler",
     },
+    {
+        "cid": "{b3c78baf-3a52-41d2-9718-c319bef9affc}",
+        "contract_ids": ["@mozilla.org/toolkit/profile-migrator;1"],
+        "esModule": "resource:///modules/MessengerContentHandler.sys.mjs",
+        "constructor": "MessengerProfileMigrator",
+    },
 ]
 
 if buildconfig.substs.get("MOZ_DEBUG") or buildconfig.substs.get("NIGHTLY_BUILD"):
@@ -69,7 +75,7 @@ if buildconfig.substs.get("MOZ_DEBUG") or buildconfig.substs.get("NIGHTLY_BUILD"
         {
             "cid": "{11c095b2-e42e-4bdf-9dd0-aed87595f6a4}",
             "contract_ids": ["@mozilla.org/test/startuprecorder;1"],
-            'esModule': "resource:///modules/StartupRecorder.sys.mjs",
+            "esModule": "resource:///modules/StartupRecorder.sys.mjs",
             "constructor": "StartupRecorder",
         },
     ]

mail/test/marionette/test_commandline.py

@@ -93,6 +93,16 @@ class TestCommandLine(MarionetteTestCase):
             [self.mail_3pane_tab],
         )
 
+    def test_migration(self):
+        """
+        Opens the import tab. We really only keep this behaviour because --migration is listed in
+        the help text.
+        """
+        self.subtest_open_tab(
+            ["--migration"],
+            [self.mail_3pane_tab, {"mode": "contentTab", "url": "about:import#start"}],
+        )
+
     def test_preferences(self):
         """Opens the preferences tab."""
         self.subtest_open_tab(