When I tried to compile my first flutter project, I observed that Initializing gradle is taking long time and never finished. So I restarted the Android Studio with Administrator Privileges and Recompiled the Project and it finished after some time.
This is how it looks in the Run window.
Launching lib\main.dart on Android SDK built for x86 in debug mode... Initializing gradle...
If you did something to resolve this issue, please share them in the comments.
Hope this helps.