Disable chrome://emoji-picker when flag is disabled.

Bug: 1166404
Change-Id: Iad9b19c47606be4be4d67771859e565653c3f0fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2627534Reviewed-by: Keith Lee <keithlee@chromium.org>
Reviewed-by: calamity <calamity@chromium.org>
Commit-Queue: Kenton Lam <kentonlam@google.com>
Cr-Commit-Position: refs/heads/master@{#844424}

chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc

@@ -786,7 +786,8 @@ WebUIFactoryFunction GetWebUIFactoryFunction(WebUI* web_ui,
       return &NewWebUI<chromeos::ArcPowerControlUI>;
     }
   }
-  if (url.host_piece() == chrome::kChromeUIEmojiPickerHost) {
+  if (url.host_piece() == chrome::kChromeUIEmojiPickerHost &&
+      base::FeatureList::IsEnabled(chromeos::features::kImeSystemEmojiPicker)) {
     return &NewWebUI<chromeos::EmojiPicker>;
   }