Hot fix for unregistered ContentSettingsType::PLUGINS.

ContentSettingsType::PLUGINS was unregistered in that CL
https://chromium-review.googlesource.com/c/chromium/src/+/2577782

This CL adds "plugins" for deprecated ContentSettingsType DCHECK.

TBR=finnur@chromium.org

Bug: 1157738
Change-Id: I860746df406892c8e6e1f94eaa6fd12eaed4958d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587036Reviewed-by: Illia Klimov <elklm@chromium.org>
Commit-Queue: Illia Klimov <elklm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837101}

chrome/browser/extensions/api/content_settings/content_settings_store.cc

@@ -341,17 +341,14 @@ void ContentSettingsStore::SetExtensionContentSettingFromList(
       // This could be if it's a string from an old settings type that has been
       // deleted. DCHECK to make sure this is the case (not some random string).
       DCHECK(content_settings_type_str == "fullscreen" ||
-             content_settings_type_str == "mouselock");
+             content_settings_type_str == "mouselock" ||
+             content_settings_type_str == "plugins");
 
       // In this case, we just skip over that setting, effectively deleting it
       // from the in-memory model. This will implicitly delete these old
       // settings from the pref store when it is written back.
       continue;
     }
-    if (content_settings_type == ContentSettingsType::PLUGINS) {
-      // Plugin content settings are no longer supported for extensions.
-      continue;
-    }
 
     const content_settings::ContentSettingsInfo* info =
         content_settings::ContentSettingsRegistry::GetInstance()->Get(