Dart plugin not installed; this adds Dart specific functionality. code example

Example 1: Flutter plugin not installed; this adds Flutter specific functionality. windows

For windows 

// run on commandline
flutter config --android-studio-dir=C:\Program Files\Android\Android Studio

Example 2: Flutter plugin not installed; this adds Flutter specific functionality

Solution that worked for me:
  1. Just install plugins.
  		Studio>>File>Settings>Plugins>Browse Repositories
  2. Search for flutter.
  3. Tap on Install (a dialog will pop regarding dart dependency. click Yes).
  4. Once the installation is finished restart android studio.

If still not worked
  1. flutter channel dev
  2. flutter doctor -v

Example 3: [!] Android Studio (version 4.1.0) X Flutter plugin not installed; this adds Flutter specific functionality. X Dart plugin not installed; this adds Dart specific functionality.

flutter channel dev
flutter channel upgrade

Example 4: Flutter plugin not installed; this adds Flutter specific functionality

ln -s ~/Library/Application\ Support/Google/AndroidStudio4.1/plugins ~/Library/Application\ Support/AndroidStudio4.1